Instrumenting internals of AccountIdFetcher::Start to locate the source of jankiness.

Instrumenting internals of AccountIdFetcher::Start to locate the source of jankiness.

Previous instrumentations showed that AccountIdFetcher::Start
alone is responsible for 20.5 janks per hour in UI thread, with 203ms average
run time. I need to instrument
the code inside it to find out which part causes jank.

This is a mechanical change that adds instrumentation required to locate the
source of jankiness (i.e. a long-running fragment of code executed as a part of
the task that causes jank) in the code. See the bug for details on what kind of
jank we are after.
A number of similar CLs were landed, and none of them caused issues. They've
helped to find and fix janky code. The code of the instrumentation is highly
optimized and is not expected to affect performance. The code simply creates a
diagnostic task which is identical to ones created by PostTask or IPC message
handlers. The task gets created only in developer build and in Canary channel.

BUG=422460
Committed: https://crrev.com/b259c8718b81478c3e5330604bb133ad50cec684
Cr-Commit-Position: refs/heads/master@{#302649}

[vadimt, 2014-11-04 01:39:59]

vadimt@chromium.org changed reviewers:
+ rogerta@chromium.org

[vadimt, 2014-11-04 01:39:59]

rogerta@, please provide OWNER's approval

[Roger Tawa OOO till Jul 10th, 2014-11-04 16:28:08]

lgtm, which one question below.

https://codereview.chromium.org/685033006/diff/1/google_apis/gaia/oauth2_toke...
File google_apis/gaia/oauth2_token_service.cc (right):

https://codereview.chromium.org/685033006/diff/1/google_apis/gaia/oauth2_toke...
google_apis/gaia/oauth2_token_service.cc:424: 
I wonder if this trace is needed given that this function simply wraps
StartRequestForClientWithContext(), which is traced below.  Is there a reason to
trace this function and not the next two below?

[vadimt, 2014-11-04 16:47:53]

https://codereview.chromium.org/685033006/diff/1/google_apis/gaia/oauth2_toke...
File google_apis/gaia/oauth2_token_service.cc (right):

https://codereview.chromium.org/685033006/diff/1/google_apis/gaia/oauth2_toke...
google_apis/gaia/oauth2_token_service.cc:424: 
On 2014/11/04 16:28:08, Roger Tawa wrote:
> I wonder if this trace is needed given that this function simply wraps
> StartRequestForClientWithContext(), which is traced below.  Is there a reason
to
> trace this function and not the next two below?

Done.

[vadimt, 2014-11-04 16:47:58]

The CQ bit was checked by vadimt@chromium.org

[commit-bot: I haz the power, 2014-11-04 16:49:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/685033006/20001

[commit-bot: I haz the power, 2014-11-04 18:20:58]

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

[commit-bot: I haz the power, 2014-11-04 18:21:00]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[vadimt, 2014-11-04 19:12:36]

The CQ bit was checked by vadimt@chromium.org

[commit-bot: I haz the power, 2014-11-04 19:14:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/685033006/20001

[commit-bot: I haz the power, 2014-11-04 20:02:28]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-11-04 20:03:21]

Patchset 2 (id:??) landed as
https://crrev.com/b259c8718b81478c3e5330604bb133ad50cec684
Cr-Commit-Position: refs/heads/master@{#302649}