Make telemetry platform a singleton

Make telemetry platform a singleton

Previously, platform backends were singletons [per platform] but the platform
object itself was created and destroyed by the browser. Moreover, the current OS backend was publicly accessible.

This patch tightens up the lifecycle of platforms, making the host platform
an explicit singleton, and target platforms singletons owned by their finder.

And, the platform backend is no longer exposed. Sadly, three corner cases exist:
a memory test case and the actual desktop-based browser finders.

R=tonyg
BUG=356763
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287739

[nduca, 2014-08-02 04:21:05]

wip but ptal in case you've got a moment to sanity check the approach. it
doesn't pass tests quite yet so i know its a bit buggy.

[tonyg, 2014-08-02 15:58:19]

This patch is trying to do a lot at once. Some parts I think are basically ready
to land, but other parts seem like a regression. Details in comments...

https://codereview.chromium.org/436873003/diff/1/tools/telemetry/telemetry/co...
File tools/telemetry/telemetry/core/browser.py (right):

https://codereview.chromium.org/436873003/diff/1/tools/telemetry/telemetry/co...
tools/telemetry/telemetry/core/browser.py:189: def cpu_stats(self):
I think the root of the problem here is that these *_stats methods don't belong
on Browser. Instead, they should be available via Timeline.

The unfortunate thing about this patch's attempt to make these first class
citizens in Platform is that it means opening up all these things in the
Platform API more widely. WDYT?

https://codereview.chromium.org/436873003/diff/1/tools/telemetry/telemetry/co...
File tools/telemetry/telemetry/core/platform/__init__.py (right):

https://codereview.chromium.org/436873003/diff/1/tools/telemetry/telemetry/co...
tools/telemetry/telemetry/core/platform/__init__.py:22: def
ResetHostPlatformSingleton():
What's the use case for resetting? I can't think of a case where the host would
change.

https://codereview.chromium.org/436873003/diff/1/tools/telemetry/telemetry/co...
tools/telemetry/telemetry/core/platform/__init__.py:30: return 'linux'
This ends up duplicating strings from the platforms themselves. Do you think we
really need the GetHostPlatformName() sugar, or is it fine to do
GetHostPlatform().GetOSName()?

https://codereview.chromium.org/436873003/diff/1/tools/telemetry/telemetry/co...
tools/telemetry/telemetry/core/platform/__init__.py:275: def GetChildPids(self,
pid):
Isn't this a backendy thing? Are we really exposing this to the API?

I know in the past we've been pretty careful about making sure Measurements are
agnostic of pids.

https://codereview.chromium.org/436873003/diff/1/tools/telemetry/telemetry/co...
tools/telemetry/telemetry/core/platform/__init__.py:281: def
WillGetMemoryStats(self):
Seems like another good thing to hide from the API. We shouldn't trust
Measurements to have to call Will/Dids at the right point, right?

[nduca, 2014-08-03 08:27:24]

I've updated this patch so its a little clearer. It does less, but has two
layering violations that previously existed:
1. the desktop browser finders reach into the host platform to get the backend,
because the browser uses it
2. the mac platform backend untitest reaches into the host platform to get the
backend.

These layering violations are suppressed with pylint-disables. I think this
patch is more landable now.

I do think these layering issues can be fixed by exposing more on the platform,
and that this can be done without sacrificing the primary goal of hiding the
browser pid, but I'm fine ignoring that for now. The most important issue for me
is making the platform a singleton, since that enables übertracing: the
ubertracer instance will hang off the platform object, I think.

[nduca, 2014-08-04 22:30:33]

friendly ping

[nduca, 2014-08-05 04:03:19]

... in search of reviewer. Being aggressive because I'm getting stuff piled up
behind this.

[tonyg, 2014-08-05 15:45:58]

lgtm

Love it. Thanks for cleaning this up.

[commit-bot: I haz the power, 2014-08-05 15:46:56]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nduca@chromium.org/436873003/60001

[commit-bot: I haz the power, 2014-08-05 19:22:40]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/42656)

[commit-bot: I haz the power, 2014-08-05 19:37:20]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-05 19:37:21]

Try jobs failed on following builders:
  win_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/42742)

[tonyg, 2014-08-05 19:39:47]

The CQ bit was checked by tonyg@chromium.org

[commit-bot: I haz the power, 2014-08-05 19:40:58]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nduca@chromium.org/436873003/60001

[commit-bot: I haz the power, 2014-08-05 19:57:32]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/42767)

[commit-bot: I haz the power, 2014-08-05 21:02:15]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-05 21:02:16]

Failed to apply patch for
tools/telemetry/telemetry/core/platform/platform_backend_unittest.py:
While running patch -p1 --forward --force --no-backup-if-mismatch;
  patching file
tools/telemetry/telemetry/core/platform/platform_backend_unittest.py
  Hunk #1 FAILED at 6.
  1 out of 1 hunk FAILED -- saving rejects to file
tools/telemetry/telemetry/core/platform/platform_backend_unittest.py.rej

Patch:      
tools/telemetry/telemetry/core/platform/platform_backend_unittest.py
Index: tools/telemetry/telemetry/core/platform/platform_backend_unittest.py
diff --git
a/tools/telemetry/telemetry/core/platform/platform_backend_unittest.py
b/tools/telemetry/telemetry/core/platform/platform_backend_unittest.py
index
d4267f7fa6c5ea30d39cf72b962c18bb3da4f1e0..a38fe000055404f324dbc56ec350fcac19a94a06
100644
--- a/tools/telemetry/telemetry/core/platform/platform_backend_unittest.py
+++ b/tools/telemetry/telemetry/core/platform/platform_backend_unittest.py
@@ -6,27 +6,27 @@ import logging
 import time
 import unittest
 
-from telemetry.core.platform import factory
+from telemetry.core import platform as platform_module
 
 
 class PlatformBackendTest(unittest.TestCase):
   def testPowerMonitoringSync(self):
     # Tests that the act of monitoring power doesn't blow up.
-    backend = factory.GetPlatformBackendForCurrentOS()
-    if not backend.CanMonitorPower():
+    platform = platform_module.GetHostPlatform()
+    if not platform.CanMonitorPower():
       logging.warning('Test not supported on this platform.')
       return
 
     browser_mock = lambda: None
     # Android needs to access the package of the monitored app.
-    if backend.GetOSName() == 'android':
+    if platform.GetOSName() == 'android':
       # pylint: disable=W0212
-      browser_mock._browser_backend = lambda: None
+      browser_mock._browser_backed = lambda: None
       # Monitor the launcher, which is always present.
       browser_mock._browser_backend.package = 'com.android.launcher'
 
-    backend.StartMonitoringPower(browser_mock)
+    platform.StartMonitoringPower(browser_mock)
     time.sleep(0.001)
-    output = backend.StopMonitoringPower()
+    output = platform.StopMonitoringPower()
     self.assertTrue(output.has_key('power_samples_mw'))
     self.assertTrue(output.has_key('identifier'))

[nduca, 2014-08-05 21:56:51]

The CQ bit was checked by nduca@chromium.org

[commit-bot: I haz the power, 2014-08-05 21:58:38]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nduca@chromium.org/436873003/80001

[commit-bot: I haz the power, 2014-08-05 23:02:51]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu/builds/...)
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/37717)
  win_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/42882)
  android_aosp on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_aosp/bu...)
  android_chromium_gn_compile_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_chromiu...)
  android_clang_dbg on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)
  android_dbg on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg/bui...)
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_gn_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)
  mac_chromium_compile_dbg on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  mac_chromium_rel on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel/...)
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)
  win_chromium_compile_dbg on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)
  win_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel/...)
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[commit-bot: I haz the power, 2014-08-05 23:05:35]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-05 23:05:36]

Try jobs failed on following builders:
  linux_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu/builds/...)
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/37740)
  android_aosp on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_aosp/bu...)
  android_dbg on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg/bui...)
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)
  mac_chromium_compile_dbg on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  mac_chromium_rel on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel/...)

[nduca, 2014-08-06 02:56:57]

The CQ bit was checked by nduca@chromium.org

[commit-bot: I haz the power, 2014-08-06 03:00:29]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nduca@chromium.org/436873003/80001

[commit-bot: I haz the power, 2014-08-06 03:23:45]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu/builds/...)
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/37814)
  win_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/42987)
  android_aosp on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_aosp/bu...)
  android_chromium_gn_compile_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_chromiu...)
  android_clang_dbg on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)
  android_dbg on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg/bui...)
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_gn_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)
  mac_chromium_compile_dbg on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  mac_chromium_rel on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel/...)
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)
  win_chromium_compile_dbg on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)
  win_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel/...)
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[commit-bot: I haz the power, 2014-08-06 03:26:06]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-06 03:26:07]

Try jobs failed on following builders:
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/37822)
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)
  mac_chromium_compile_dbg on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  mac_chromium_rel on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel/...)
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)

[nduca, 2014-08-06 04:40:00]

The CQ bit was checked by nduca@chromium.org

[commit-bot: I haz the power, 2014-08-06 04:41:25]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nduca@chromium.org/436873003/100001

[commit-bot: I haz the power, 2014-08-06 09:08:52]

Change committed as 287739