third_party/blink/renderer/platform/loader/fetch/resource_load_scheduler.h - chromium/src - Git at Google

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_LOADER_FETCH_RESOURCE_LOAD_SCHEDULER_H_
 #define THIRD_PARTY_BLINK_RENDERER_PLATFORM_LOADER_FETCH_RESOURCE_LOAD_SCHEDULER_H_

 #include <map>
 #include <set>

 #include "third_party/blink/renderer/platform/heap/garbage_collected.h"
 #include "third_party/blink/renderer/platform/heap/heap_allocator.h"
 #include "third_party/blink/renderer/platform/loader/fetch/resource.h"
 #include "third_party/blink/renderer/platform/loader/fetch/resource_loader_options.h"
 #include "third_party/blink/renderer/platform/scheduler/public/frame_scheduler.h"
 #include "third_party/blink/renderer/platform/wtf/hash_set.h"

 namespace blink {

 class ConsoleLogger;
 class FetchContext;

 // Client interface to use the throttling/scheduling functionality that
 // ResourceLoadScheduler provides.
 class PLATFORM_EXPORT ResourceLoadSchedulerClient
     : public GarbageCollectedMixin {
  public:
   // Called when the request is granted to run.
   virtual void Run() = 0;

   void Trace(blink::Visitor* visitor) override {}
 };

 // ResourceLoadScheduler provides a unified per-frame infrastructure to schedule
 // loading requests. When Request() is called with a
 // ResourceLoadSchedulerClient |client|, it calls |client|'s Run() method
 // synchronously or asynchronously to notify that |client| can start loading.
 //
 // A ResourceLoadScheduler may initiate a new resource loading in the following
 // cases:
 // - When Request() is called
 // - When LoosenThrottlingPolicy() is called
 // - When SetPriority() is called
 // - When Release() is called with kReleaseAndSchedule
 // - When OnThrottlingStateChanged() is called
 //
 // A ResourceLoadScheduler determines if a request can be throttleable or not,
 // and keeps track of pending throttleable requests with priority information
 // (i.e., ResourceLoadPriority accompanied with an integer called
 // "intra-priority"). Here are the general principles:
 //  - A ResourceLoadScheduler does not throttle requests that cannot be
 //    throttleable. It will call client's Run() method as soon as possible.
 //  - A ResourceLoadScheduler determines whether a request can be throttleable
 //    by seeing Request()'s ThrottleOption argument and requests' priority
 //    information. Requests' priority information can be modified via
 //    SetPriority().
 //  - A ResourceLoadScheulder won't initiate a new resource loading which can
 //    be throttleable when there are more active throttleable requests loading
 //    activities more than its internal threshold (i.e., what
 //    GetOutstandingLimit() returns)".
 //
 //  ResourceLoadScheduler has two modes each of which has its own threshold.
 //   - Tight mode (used until the frame sees a <body> element):
 //     ResourceLoadScheduler considers a request throttleable if its priority
 //     is less than |kHigh|.
 //   - Normal mode:
 //     ResourceLoadScheduler considers a request throttleable if its priority
 //     is less than |kMedium|.
 //
 // Here are running experiments (as of M65):
 //  - "ResourceLoadScheduler"
 //   - Resource loading requests are not at throttled when the frame is in
 //     the foreground tab.
 //   - Resource loading requests are throttled when the frame is in a
 //     background tab. It has different thresholds for the main frame
 //     and sub frames. When the frame has been background for more than five
 //     minutes, all throttleable resource loading requests are throttled
 //     indefinitely (i.e., threshold is zero in such a circumstance).
 class PLATFORM_EXPORT ResourceLoadScheduler final
     : public GarbageCollectedFinalized<ResourceLoadScheduler>,
       public FrameScheduler::Observer {
   WTF_MAKE_NONCOPYABLE(ResourceLoadScheduler);

  public:
   // An option to use in calling Request(). If kCanNotBeStoppedOrThrottled is
   // specified, the request should be granted and Run() should be called
   // synchronously. If kStoppable is specified, Run() will be called immediately
   // unless resource loading is stopped. Otherwise, OnRequestGranted() could be
   // called later when other outstanding requests are finished.
   enum class ThrottleOption {
     kThrottleable = 0,
     kStoppable = 1,
     kCanNotBeStoppedOrThrottled = 2,
   };

   // An option to use in calling Release(). If kReleaseOnly is specified,
   // the specified request should be released, but no other requests should
   // be scheduled within the call.
   enum class ReleaseOption { kReleaseOnly, kReleaseAndSchedule };

   // A class to pass traffic report hints on calling Release().
   class TrafficReportHints {
    public:
     // |encoded_data_length| is payload size in bytes sent over the network.
     // |decoded_body_length| is received resource data size in bytes.
     TrafficReportHints(int64_t encoded_data_length, int64_t decoded_body_length)
         : valid_(true),
           encoded_data_length_(encoded_data_length),
           decoded_body_length_(decoded_body_length) {}

     // Returns the instance that represents an invalid report, which can be
     // used when a caller don't want to report traffic, i.e. on a failure.
     static PLATFORM_EXPORT TrafficReportHints InvalidInstance() {
       return TrafficReportHints();
     }

     bool IsValid() const { return valid_; }

     int64_t encoded_data_length() const {
       DCHECK(valid_);
       return encoded_data_length_;
     }
     int64_t decoded_body_length() const {
       DCHECK(valid_);
       return decoded_body_length_;
     }

    private:
     // Default constructor makes an invalid instance that won't be recorded.
     TrafficReportHints() = default;

     bool valid_ = false;
     int64_t encoded_data_length_ = 0;
     int64_t decoded_body_length_ = 0;
   };

   // ResourceLoadScheduler has two policies: |kTight| and |kNormal|. Currently
   // this is used to support aggressive throttling while the corresponding frame
   // is in layout-blocking phase. There is only one state transition,
   // |kTight| => |kNormal|, which is done by |LoosenThrottlingPolicy|.
   enum class ThrottlingPolicy { kTight, kNormal };

   // Returned on Request(). Caller should need to return it via Release().
   using ClientId = uint64_t;

   static constexpr ClientId kInvalidClientId = 0u;

   static constexpr size_t kOutstandingUnlimited =
       std::numeric_limits<size_t>::max();

   static ResourceLoadScheduler* Create(FetchContext*);

   ResourceLoadScheduler(FetchContext*);
   ~ResourceLoadScheduler() override;

   void Trace(blink::Visitor*);

   // Changes the policy from |kTight| to |kNormal|. This function can be called
   // multiple times, and does nothing when the scheduler is already working with
   // the normal policy. This function may initiate a new resource loading.
   void LoosenThrottlingPolicy();

   // Stops all operations including observing throttling signals.
   // ResourceLoadSchedulerClient::Run() will not be called once this method is
   // called. This method can be called multiple times safely.
   void Shutdown();

   // Makes a request. This may synchronously call
   // ResourceLoadSchedulerClient::Run(), but it is guaranteed that ClientId is
   // populated before ResourceLoadSchedulerClient::Run() is called, so that the
   // caller can call Release() with the assigned ClientId correctly.
   void Request(ResourceLoadSchedulerClient*,
                ThrottleOption,
                ResourceLoadPriority,
                int intra_priority,
                ConsoleLogger* console_logger,
                ClientId*);

   // Updates the priority information of the given client. This function may
   // initiate a new resource loading.
   void SetPriority(ClientId, ResourceLoadPriority, int intra_priority);

   // ResourceLoadSchedulerClient should call this method when the loading is
   // finished, or canceled. This method can be called in a pre-finalization
   // step, bug the ReleaseOption must be kReleaseOnly in such a case.
   // TrafficReportHints is for reporting histograms.
   // TrafficReportHints::InvalidInstance() can be used to omit reporting.
   bool Release(ClientId, ReleaseOption, const TrafficReportHints&);

   // Checks if the specified client was already scheduled to call Run(), but
   // haven't call Release() yet.
   bool IsRunning(ClientId id) { return running_requests_.Contains(id); }

   // Sets outstanding limit for testing.
   void SetOutstandingLimitForTesting(size_t limit) {
     SetOutstandingLimitForTesting(limit, limit);
   }
   void SetOutstandingLimitForTesting(size_t tight_limit, size_t normal_limit);

   void OnNetworkQuiet();

   // FrameScheduler::Observer overrides:
   void OnLifecycleStateChanged(scheduler::SchedulingLifecycleState) override;

  private:
   class TrafficMonitor;

   class ClientIdWithPriority {
    public:
     struct Compare {
       bool operator()(const ClientIdWithPriority& x,
                       const ClientIdWithPriority& y) const {
         if (x.priority != y.priority)
           return x.priority > y.priority;
         if (x.intra_priority != y.intra_priority)
           return x.intra_priority > y.intra_priority;
         return x.client_id < y.client_id;
       }
     };

     ClientIdWithPriority(ClientId client_id,
                          WebURLRequest::Priority priority,
                          int intra_priority)
         : client_id(client_id),
           priority(priority),
           intra_priority(intra_priority) {}

     const ClientId client_id;
     const WebURLRequest::Priority priority;
     const int intra_priority;
   };

   struct ClientInfo : public GarbageCollected<ClientInfo> {
     ClientInfo(ResourceLoadSchedulerClient* client,
                ThrottleOption option,
                ResourceLoadPriority priority,
                int intra_priority)
         : client(client),
           option(option),
           priority(priority),
           intra_priority(intra_priority) {}

     void Trace(blink::Visitor* visitor) { visitor->Trace(client); }

     Member<ResourceLoadSchedulerClient> client;
     ThrottleOption option;
     ResourceLoadPriority priority;
     int intra_priority;
   };

   // Gets the highest priority pending request that is allowed to be run.
   bool GetNextPendingRequest(ClientId* id);

   // Returns whether we can throttle a request with the given client info based
   // on life cycle state.
   bool IsClientDelayable(const ClientIdWithPriority& info,
                          ThrottleOption option) const;

   // Generates the next ClientId.
   ClientId GenerateClientId();

   // Picks up one client if there is a budget and route it to run.
   void MaybeRun();

   // Grants a client to run,
   void Run(ClientId, ResourceLoadSchedulerClient*, bool throttleable);

   size_t GetOutstandingLimit() const;

   bool IsThrottledState() const;

   // A flag to indicate an internal running state.
   // TODO(toyoshim): We may want to use enum once we start to have more states.
   bool is_shutdown_ = false;

   ThrottlingPolicy policy_ = ThrottlingPolicy::kNormal;

   // ResourceLoadScheduler threshold values for various circumstances. Some
   // conditions can overlap, and ResourceLoadScheduler chooses the smallest
   // value in such cases.

   // Used when |policy_| is |kTight|.
   size_t tight_outstanding_limit_ = kOutstandingUnlimited;

   // Used when |policy_| is |kNormal|.
   size_t normal_outstanding_limit_ = kOutstandingUnlimited;

   // Used when |frame_scheduler_throttling_state_| is |kThrottled|.
   const size_t outstanding_limit_for_throttled_frame_scheduler_;

   // The last used ClientId to calculate the next.
   ClientId current_id_ = kInvalidClientId;

   // Holds clients that were granted and are running.
   HashSet<ClientId> running_requests_;

   HashSet<ClientId> running_throttleable_requests_;

   // Largest number of running requests seen so far.
   unsigned maximum_running_requests_seen_ = 0;

   // Holds a flag to omit repeating console messages. Will be reset on
   // SchedulingLifecycleState changes.
   bool omit_console_log_ = false;

   enum class ThrottlingHistory {
     kInitial,
     kThrottled,
     kNotThrottled,
     kPartiallyThrottled,
     kStopped,
   };
   ThrottlingHistory throttling_history_ = ThrottlingHistory::kInitial;
   scheduler::SchedulingLifecycleState frame_scheduler_lifecycle_state_ =
       scheduler::SchedulingLifecycleState::kNotThrottled;

   // Holds clients that haven't been granted, and are waiting for a grant.
   HeapHashMap<ClientId, Member<ClientInfo>> pending_request_map_;
   // We use std::set here because WTF doesn't have its counterpart.
   // This tracks two sets of requests, throttleable and stoppable.
   std::map<ThrottleOption,
            std::set<ClientIdWithPriority, ClientIdWithPriority::Compare>>
       pending_requests_;

   // Holds an internal class instance to monitor and report traffic.
   std::unique_ptr<TrafficMonitor> traffic_monitor_;

   // Holds FetchContext reference to contact FrameScheduler.
   Member<FetchContext> context_;

   // Handle to throttling observer.
   std::unique_ptr<FrameScheduler::LifecycleObserverHandle>
       scheduler_observer_handle_;
 };

 }  // namespace blink

 #endif
	// Copyright 2017 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_LOADER_FETCH_RESOURCE_LOAD_SCHEDULER_H_
	#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_LOADER_FETCH_RESOURCE_LOAD_SCHEDULER_H_

	#include <map>
	#include <set>

	#include "third_party/blink/renderer/platform/heap/garbage_collected.h"
	#include "third_party/blink/renderer/platform/heap/heap_allocator.h"
	#include "third_party/blink/renderer/platform/loader/fetch/resource.h"
	#include "third_party/blink/renderer/platform/loader/fetch/resource_loader_options.h"
	#include "third_party/blink/renderer/platform/scheduler/public/frame_scheduler.h"
	#include "third_party/blink/renderer/platform/wtf/hash_set.h"

	namespace blink {

	class ConsoleLogger;
	class FetchContext;

	// Client interface to use the throttling/scheduling functionality that
	// ResourceLoadScheduler provides.
	class PLATFORM_EXPORT ResourceLoadSchedulerClient
	: public GarbageCollectedMixin {
	public:
	// Called when the request is granted to run.
	virtual void Run() = 0;

	void Trace(blink::Visitor* visitor) override {}
	};

	// ResourceLoadScheduler provides a unified per-frame infrastructure to schedule
	// loading requests. When Request() is called with a
	// ResourceLoadSchedulerClient \|client\|, it calls \|client\|'s Run() method
	// synchronously or asynchronously to notify that \|client\| can start loading.
	//
	// A ResourceLoadScheduler may initiate a new resource loading in the following
	// cases:
	// - When Request() is called
	// - When LoosenThrottlingPolicy() is called
	// - When SetPriority() is called
	// - When Release() is called with kReleaseAndSchedule
	// - When OnThrottlingStateChanged() is called
	//
	// A ResourceLoadScheduler determines if a request can be throttleable or not,
	// and keeps track of pending throttleable requests with priority information
	// (i.e., ResourceLoadPriority accompanied with an integer called
	// "intra-priority"). Here are the general principles:
	// - A ResourceLoadScheduler does not throttle requests that cannot be
	// throttleable. It will call client's Run() method as soon as possible.
	// - A ResourceLoadScheduler determines whether a request can be throttleable
	// by seeing Request()'s ThrottleOption argument and requests' priority
	// information. Requests' priority information can be modified via
	// SetPriority().
	// - A ResourceLoadScheulder won't initiate a new resource loading which can
	// be throttleable when there are more active throttleable requests loading
	// activities more than its internal threshold (i.e., what
	// GetOutstandingLimit() returns)".
	//
	// ResourceLoadScheduler has two modes each of which has its own threshold.
	// - Tight mode (used until the frame sees a <body> element):
	// ResourceLoadScheduler considers a request throttleable if its priority
	// is less than \|kHigh\|.
	// - Normal mode:
	// ResourceLoadScheduler considers a request throttleable if its priority
	// is less than \|kMedium\|.
	//
	// Here are running experiments (as of M65):
	// - "ResourceLoadScheduler"
	// - Resource loading requests are not at throttled when the frame is in
	// the foreground tab.
	// - Resource loading requests are throttled when the frame is in a
	// background tab. It has different thresholds for the main frame
	// and sub frames. When the frame has been background for more than five
	// minutes, all throttleable resource loading requests are throttled
	// indefinitely (i.e., threshold is zero in such a circumstance).
	class PLATFORM_EXPORT ResourceLoadScheduler final
	: public GarbageCollectedFinalized<ResourceLoadScheduler>,
	public FrameScheduler::Observer {
	WTF_MAKE_NONCOPYABLE(ResourceLoadScheduler);

	public:
	// An option to use in calling Request(). If kCanNotBeStoppedOrThrottled is
	// specified, the request should be granted and Run() should be called
	// synchronously. If kStoppable is specified, Run() will be called immediately
	// unless resource loading is stopped. Otherwise, OnRequestGranted() could be
	// called later when other outstanding requests are finished.
	enum class ThrottleOption {
	kThrottleable = 0,
	kStoppable = 1,
	kCanNotBeStoppedOrThrottled = 2,
	};

	// An option to use in calling Release(). If kReleaseOnly is specified,
	// the specified request should be released, but no other requests should
	// be scheduled within the call.
	enum class ReleaseOption { kReleaseOnly, kReleaseAndSchedule };

	// A class to pass traffic report hints on calling Release().
	class TrafficReportHints {
	public:
	// \|encoded_data_length\| is payload size in bytes sent over the network.
	// \|decoded_body_length\| is received resource data size in bytes.
	TrafficReportHints(int64_t encoded_data_length, int64_t decoded_body_length)
	: valid_(true),
	encoded_data_length_(encoded_data_length),
	decoded_body_length_(decoded_body_length) {}

	// Returns the instance that represents an invalid report, which can be
	// used when a caller don't want to report traffic, i.e. on a failure.
	static PLATFORM_EXPORT TrafficReportHints InvalidInstance() {
	return TrafficReportHints();
	}

	bool IsValid() const { return valid_; }

	int64_t encoded_data_length() const {
	DCHECK(valid_);
	return encoded_data_length_;
	}
	int64_t decoded_body_length() const {
	DCHECK(valid_);
	return decoded_body_length_;
	}

	private:
	// Default constructor makes an invalid instance that won't be recorded.
	TrafficReportHints() = default;

	bool valid_ = false;
	int64_t encoded_data_length_ = 0;
	int64_t decoded_body_length_ = 0;
	};

	// ResourceLoadScheduler has two policies: \|kTight\| and \|kNormal\|. Currently
	// this is used to support aggressive throttling while the corresponding frame
	// is in layout-blocking phase. There is only one state transition,
	// \|kTight\| => \|kNormal\|, which is done by \|LoosenThrottlingPolicy\|.
	enum class ThrottlingPolicy { kTight, kNormal };

	// Returned on Request(). Caller should need to return it via Release().
	using ClientId = uint64_t;

	static constexpr ClientId kInvalidClientId = 0u;

	static constexpr size_t kOutstandingUnlimited =
	std::numeric_limits<size_t>::max();

	static ResourceLoadScheduler* Create(FetchContext*);

	ResourceLoadScheduler(FetchContext*);
	~ResourceLoadScheduler() override;

	void Trace(blink::Visitor*);

	// Changes the policy from \|kTight\| to \|kNormal\|. This function can be called
	// multiple times, and does nothing when the scheduler is already working with
	// the normal policy. This function may initiate a new resource loading.
	void LoosenThrottlingPolicy();

	// Stops all operations including observing throttling signals.
	// ResourceLoadSchedulerClient::Run() will not be called once this method is
	// called. This method can be called multiple times safely.
	void Shutdown();

	// Makes a request. This may synchronously call
	// ResourceLoadSchedulerClient::Run(), but it is guaranteed that ClientId is
	// populated before ResourceLoadSchedulerClient::Run() is called, so that the
	// caller can call Release() with the assigned ClientId correctly.
	void Request(ResourceLoadSchedulerClient*,
	ThrottleOption,
	ResourceLoadPriority,
	int intra_priority,
	ConsoleLogger* console_logger,
	ClientId*);

	// Updates the priority information of the given client. This function may
	// initiate a new resource loading.
	void SetPriority(ClientId, ResourceLoadPriority, int intra_priority);

	// ResourceLoadSchedulerClient should call this method when the loading is
	// finished, or canceled. This method can be called in a pre-finalization
	// step, bug the ReleaseOption must be kReleaseOnly in such a case.
	// TrafficReportHints is for reporting histograms.
	// TrafficReportHints::InvalidInstance() can be used to omit reporting.
	bool Release(ClientId, ReleaseOption, const TrafficReportHints&);

	// Checks if the specified client was already scheduled to call Run(), but
	// haven't call Release() yet.
	bool IsRunning(ClientId id) { return running_requests_.Contains(id); }

	// Sets outstanding limit for testing.
	void SetOutstandingLimitForTesting(size_t limit) {
	SetOutstandingLimitForTesting(limit, limit);
	}
	void SetOutstandingLimitForTesting(size_t tight_limit, size_t normal_limit);

	void OnNetworkQuiet();

	// FrameScheduler::Observer overrides:
	void OnLifecycleStateChanged(scheduler::SchedulingLifecycleState) override;

	private:
	class TrafficMonitor;

	class ClientIdWithPriority {
	public:
	struct Compare {
	bool operator()(const ClientIdWithPriority& x,
	const ClientIdWithPriority& y) const {
	if (x.priority != y.priority)
	return x.priority > y.priority;
	if (x.intra_priority != y.intra_priority)
	return x.intra_priority > y.intra_priority;
	return x.client_id < y.client_id;
	}
	};

	ClientIdWithPriority(ClientId client_id,
	WebURLRequest::Priority priority,
	int intra_priority)
	: client_id(client_id),
	priority(priority),
	intra_priority(intra_priority) {}

	const ClientId client_id;
	const WebURLRequest::Priority priority;
	const int intra_priority;
	};

	struct ClientInfo : public GarbageCollected<ClientInfo> {
	ClientInfo(ResourceLoadSchedulerClient* client,
	ThrottleOption option,
	ResourceLoadPriority priority,
	int intra_priority)
	: client(client),
	option(option),
	priority(priority),
	intra_priority(intra_priority) {}

	void Trace(blink::Visitor* visitor) { visitor->Trace(client); }

	Member<ResourceLoadSchedulerClient> client;
	ThrottleOption option;
	ResourceLoadPriority priority;
	int intra_priority;
	};

	// Gets the highest priority pending request that is allowed to be run.
	bool GetNextPendingRequest(ClientId* id);

	// Returns whether we can throttle a request with the given client info based
	// on life cycle state.
	bool IsClientDelayable(const ClientIdWithPriority& info,
	ThrottleOption option) const;

	// Generates the next ClientId.
	ClientId GenerateClientId();

	// Picks up one client if there is a budget and route it to run.
	void MaybeRun();

	// Grants a client to run,
	void Run(ClientId, ResourceLoadSchedulerClient*, bool throttleable);

	size_t GetOutstandingLimit() const;

	bool IsThrottledState() const;

	// A flag to indicate an internal running state.
	// TODO(toyoshim): We may want to use enum once we start to have more states.
	bool is_shutdown_ = false;

	ThrottlingPolicy policy_ = ThrottlingPolicy::kNormal;

	// ResourceLoadScheduler threshold values for various circumstances. Some
	// conditions can overlap, and ResourceLoadScheduler chooses the smallest
	// value in such cases.

	// Used when \|policy_\| is \|kTight\|.
	size_t tight_outstanding_limit_ = kOutstandingUnlimited;

	// Used when \|policy_\| is \|kNormal\|.
	size_t normal_outstanding_limit_ = kOutstandingUnlimited;

	// Used when \|frame_scheduler_throttling_state_\| is \|kThrottled\|.
	const size_t outstanding_limit_for_throttled_frame_scheduler_;

	// The last used ClientId to calculate the next.
	ClientId current_id_ = kInvalidClientId;

	// Holds clients that were granted and are running.
	HashSet<ClientId> running_requests_;

	HashSet<ClientId> running_throttleable_requests_;

	// Largest number of running requests seen so far.
	unsigned maximum_running_requests_seen_ = 0;

	// Holds a flag to omit repeating console messages. Will be reset on
	// SchedulingLifecycleState changes.
	bool omit_console_log_ = false;

	enum class ThrottlingHistory {
	kInitial,
	kThrottled,
	kNotThrottled,
	kPartiallyThrottled,
	kStopped,
	};
	ThrottlingHistory throttling_history_ = ThrottlingHistory::kInitial;
	scheduler::SchedulingLifecycleState frame_scheduler_lifecycle_state_ =
	scheduler::SchedulingLifecycleState::kNotThrottled;

	// Holds clients that haven't been granted, and are waiting for a grant.
	HeapHashMap<ClientId, Member<ClientInfo>> pending_request_map_;
	// We use std::set here because WTF doesn't have its counterpart.
	// This tracks two sets of requests, throttleable and stoppable.
	std::map<ThrottleOption,
	std::set<ClientIdWithPriority, ClientIdWithPriority::Compare>>
	pending_requests_;

	// Holds an internal class instance to monitor and report traffic.
	std::unique_ptr<TrafficMonitor> traffic_monitor_;

	// Holds FetchContext reference to contact FrameScheduler.
	Member<FetchContext> context_;

	// Handle to throttling observer.
	std::unique_ptr<FrameScheduler::LifecycleObserverHandle>
	scheduler_observer_handle_;
	};

	} // namespace blink

	#endif