Scheduler: Add FrameOrWorkerGlobalScopeScheduler

This CL adds FrameOrWorkerGlobalScopeScheduler that is the base class of
FrameScheduler and WorkerGlobalScopeScheduler. A motivation of this change is to
abstract those schedulers for ExecutionContext-agnostic implementation. As an
example, this CL changes access to the scheduler in WebSocket.

Bug: 825740
Change-Id: Ie03869d35b502082e172672dad451720c31a937a
Reviewed-on: https://chromium-review.googlesource.com/994552
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hajime Hoshi <hajimehoshi@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549175}
15 files changed