Implement TracingController::GetMonitoringStatus

Implement TracingController::GetMonitoringStatus

trace-viewer side CL is here: https://codereview.appspot.com/52710047

Currently the monitoring mode doesn't work correctly when we reload about:tracing. This is because reloaded about:tracing fails in extracting the current monitoring status (See my comment in patch set 2).

This CL implements TracingController::GetMonitoringStatus so that trace-viewer/src/about_tracing/profiling_view.js can get the current monitoring status when loading the profiling view.

TEST=content_browsertests::EnableCaptureAndDisableMonitoring
R=nduca@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=245211

[haraken, 2014-01-16 02:32:14]

PTAL.

https://codereview.chromium.org/139313005/diff/30001/content/browser/tracing/...
File content/browser/tracing/tracing_controller_impl.cc (left):

https://codereview.chromium.org/139313005/diff/30001/content/browser/tracing/...
content/browser/tracing/tracing_controller_impl.cc:790:
tracing_ui->OnMonitoringStateChanged(is_monitoring_);

I expected that this will fire window.onMonitoringStateChanged in
profiling_view.js, but it didn't work. This is because profiling_view.js is not
initialized at this point.

Alternatively, we need to implement TracingController::GetMonitoringStatus and
make profiling_view.js call it when starting about:tracing.

[nduca, 2014-01-16 03:12:32]

lgtm

[commit-bot: I haz the power, 2014-01-16 03:17:05]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/haraken@chromium.org/139313005/30001

[commit-bot: I haz the power, 2014-01-16 03:39:56]

Retried try job too often on win_rel for step(s) base_unittests, browser_tests,
interactive_ui_tests, net_unittests, unit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[commit-bot: I haz the power, 2014-01-16 03:49:16]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/haraken@chromium.org/139313005/30001

[commit-bot: I haz the power, 2014-01-16 05:34:20]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/haraken@chromium.org/139313005/360001

[haraken, 2014-01-16 16:12:20]

Looks like the failures in *_swarm_triggered are flakes.

[haraken, 2014-01-16 16:13:05]

Committed patchset #3 manually as r245211 (presubmit successful).