Remove Telemetry's Chrome tracing dependency on having a BrowserBackend.

Remove Telemetry's Chrome tracing dependency on BrowserBackend.
TracingController now directly communicates with DevToolsClientBackend
instead.

This allows us to use TracingController on Android app as well.

BUG=443897
Committed: https://crrev.com/f0942032455ca36a68d020b5c86bc70304cb0357
Cr-Commit-Position: refs/heads/master@{#311315}

[chrishenry, 2015-01-09 23:19:56]

Patchset #1 (id:1) has been deleted

[chrishenry, 2015-01-10 00:35:21]

Patchset #2 (id:40001) has been deleted

[chrishenry, 2015-01-10 00:36:30]

chrishenry@google.com changed reviewers:
+ nednguyen@google.com, sullivan@chromium.org, tonyg@chromium.org

[nednguyen, 2015-01-12 17:21:27]

https://codereview.chromium.org/842303002/diff/80001/tools/telemetry/telemetr...
File tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
(right):

https://codereview.chromium.org/842303002/diff/80001/tools/telemetry/telemetr...
tools/telemetry/telemetry/core/platform/tracing_controller_backend.py:53: if
self._current_trace_options.enable_chrome_trace:
Don't we need to remove stale devtool clients here to? Or do you think telemetry
should raise exception in this case?

[nednguyen, 2015-01-12 17:37:52]

nednguyen@google.com changed reviewers:
+ nduca@chromium.org

[nednguyen, 2015-01-12 17:37:53]

@Nat:
This chrome tracing situation is quite messy. This is the best Chris & me can
come up with to deal with the fact that start & stop tracing is a platform level
API rather than browser/webview level API. 
Do you see any medium term work we can do on Chrome side to make this less ugly?
i.e: chrome augment its trace to system trace, or serialize to a file on the
system.. ?

[chrishenry, 2015-01-12 23:45:37]

https://codereview.chromium.org/842303002/diff/80001/tools/telemetry/telemetr...
File tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
(right):

https://codereview.chromium.org/842303002/diff/80001/tools/telemetry/telemetr...
tools/telemetry/telemetry/core/platform/tracing_controller_backend.py:53: if
self._current_trace_options.enable_chrome_trace:
On 2015/01/12 17:21:27, nednguyen wrote:
> Don't we need to remove stale devtool clients here to? Or do you think
telemetry
> should raise exception in this case?

I want to raise exception, since it means we lose data.

[nednguyen, 2015-01-13 16:12:00]

https://codereview.chromium.org/842303002/diff/80001/tools/telemetry/telemetr...
File tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
(right):

https://codereview.chromium.org/842303002/diff/80001/tools/telemetry/telemetr...
tools/telemetry/telemetry/core/platform/tracing_controller_backend.py:53: if
self._current_trace_options.enable_chrome_trace:
On 2015/01/12 23:45:37, chrishenry wrote:
> On 2015/01/12 17:21:27, nednguyen wrote:
> > Don't we need to remove stale devtool clients here to? Or do you think
> telemetry
> > should raise exception in this case?
> 
> I want to raise exception, since it means we lose data.

Yeah, I think this is probably best. Another reason is webview may always crash
between the stale check & StopTracing, hence doing stale checking here is not
that bullet proof anyway.

https://codereview.chromium.org/842303002/diff/100001/tools/telemetry/telemet...
File tools/telemetry/telemetry/core/platform/tracing_controller_backend.py
(right):

https://codereview.chromium.org/842303002/diff/100001/tools/telemetry/telemet...
tools/telemetry/telemetry/core/platform/tracing_controller_backend.py:89: def
DidStartBrowser(self, browser, browser_backend):
Kill these methods?

[nednguyen, 2015-01-13 18:21:47]

lgtm

[chrishenry, 2015-01-13 18:22:06]

The CQ bit was checked by chrishenry@google.com

[commit-bot: I haz the power, 2015-01-13 18:23:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/842303002/100001

[commit-bot: I haz the power, 2015-01-13 20:01:14]

Committed patchset #4 (id:100001)

[commit-bot: I haz the power, 2015-01-13 20:02:44]

Patchset 4 (id:??) landed as
https://crrev.com/f0942032455ca36a68d020b5c86bc70304cb0357
Cr-Commit-Position: refs/heads/master@{#311315}