StackSamplingProfiler: collect partial bursts if the profiler is stopped early

StackSamplingProfiler: collect partial bursts if the profiler is stopped early

Changes the profiler behavior to retain collected samples when the
profiler is stopped in the middle of collecting a burst of samples. This
behavior is desirable for janky task collection, where we would like to
collect up to the point the task completes, but don't know beforehand
how long it will take. It's also mildly beneficial for startup profiling
in that it allows collection of profiles if Chrome is shut down shortly
after being started.

BUG=464929
Committed: https://crrev.com/0716a8fedf45c6ecff8b249da926034c34a8ea02
Cr-Commit-Position: refs/heads/master@{#346558}

[Mike Wittman, 2015-08-26 17:55:36]

wittman@chromium.org changed reviewers:
+ cpu@chromium.org

[Mike Wittman, 2015-08-26 17:55:36]

PTAL

[cpu_(ooo_6.6-7.5), 2015-09-01 00:23:17]

it was lost on me why returning void is better. I liked it better when it was
returning the bool.

But anyhow lgtm. Up to you if you want to do that.

[Mike Wittman, 2015-09-01 00:33:02]

On 2015/09/01 00:23:17, cpu wrote:
> it was lost on me why returning void is better. I liked it better when it was
> returning the bool.
> 
> But anyhow lgtm. Up to you if you want to do that.

Thanks. I don't think it's a make or break thing either way, but my thought was
that the value of the bool implies success or failure of CollectProfile to
collect the profile. With this change it's always successful, but the calling
function still needs to know whether collection was stopped so it can act
accordingly.

[Mike Wittman, 2015-09-01 00:33:13]

The CQ bit was checked by wittman@chromium.org

[commit-bot: I haz the power, 2015-09-01 00:33:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1316153002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1316153002/1

[commit-bot: I haz the power, 2015-09-01 01:16:07]

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

[commit-bot: I haz the power, 2015-09-01 01:16:08]

Try jobs failed on following builders:
  win_chromium_x64_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[Mike Wittman, 2015-09-01 01:17:36]

The CQ bit was checked by wittman@chromium.org

[commit-bot: I haz the power, 2015-09-01 01:17:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1316153002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1316153002/1

[commit-bot: I haz the power, 2015-09-01 02:23:39]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-01 02:24:06]

Patchset 1 (id:??) landed as
https://crrev.com/0716a8fedf45c6ecff8b249da926034c34a8ea02
Cr-Commit-Position: refs/heads/master@{#346558}