Add DevToolsAgent::{enable,disable}Tracing

Add DevToolsAgent::{enable,disable}Tracing

This adds support for synchronously enabling/disabling tracing in
devtools agent, so we can support tracing-based timeline enabled
synchronously from the inspected renderer.

BUG=361045
R=pfeldman@chromium.org, yurys@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266146

[pfeldman, 2014-04-21 17:50:52]

lgtm

https://codereview.chromium.org/243103008/diff/1/content/renderer/devtools/de...
File content/renderer/devtools/devtools_agent.cc (right):

https://codereview.chromium.org/243103008/diff/1/content/renderer/devtools/de...
content/renderer/devtools/devtools_agent.cc:168: TraceLog::RECORD_UNTIL_FULL);
nit: do you want to pass this as a parameter?

[yurys, 2014-04-22 07:44:28]

I'd rather we handled this in TracingAgent in the renderer: 
1) Tracing.start is first handled in the render process which replies with a
token identifying inspected instance.
2) When the response is routed in the browser process, devtools_tracing_handler
intercepts this response starts tracing in all render processes and forwards the
response to the front-end.
WDYT?

[pfeldman, 2014-04-22 07:48:08]

I like yurys's plan.

[caseq, 2014-04-22 11:06:03]

So what do we do with console.startTimeline()?

[yurys, 2014-04-22 11:47:39]

lgtm

[caseq, 2014-04-24 06:22:39]

The CQ bit was checked by caseq@chromium.org

[commit-bot: I haz the power, 2014-04-24 06:22:45]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/caseq@chromium.org/243103008/1

[commit-bot: I haz the power, 2014-04-24 08:27:35]

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

[commit-bot: I haz the power, 2014-04-24 08:27:35]

Try jobs failed on following builders:
  tryserver.chromium on chromium_presubmit
  tryserver.chromium on linux_chromium_chromeos_rel

[caseq, 2014-04-24 13:15:51]

The CQ bit was checked by caseq@chromium.org

[caseq, 2014-04-24 13:33:38]

The CQ bit was unchecked by caseq@chromium.org

[caseq, 2014-04-24 13:33:43]

The CQ bit was checked by caseq@chromium.org

[commit-bot: I haz the power, 2014-04-24 13:34:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/caseq@chromium.org/243103008/20001

[commit-bot: I haz the power, 2014-04-24 15:54:12]

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

[commit-bot: I haz the power, 2014-04-24 15:54:13]

Try jobs failed on following builders:
  tryserver.chromium on win_chromium_rel

[caseq, 2014-04-24 17:01:00]

The CQ bit was checked by caseq@chromium.org

[commit-bot: I haz the power, 2014-04-24 17:02:18]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/caseq@chromium.org/243103008/20001

[commit-bot: I haz the power, 2014-04-24 21:07:03]

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

[commit-bot: I haz the power, 2014-04-24 21:07:04]

Try jobs failed on following builders:
  tryserver.chromium on linux_chromium_chromeos_rel

[caseq, 2014-04-25 07:20:18]

Committed patchset #2 manually as r266146 (presubmit successful).