Add CollectSample API function to CpuProfiler

Add CollectSample API function to CpuProfiler

It allows embedder to inject a stack sample on demand.

BUG=chromium:579191
LOG=N

Committed: https://crrev.com/7068caf5fd614bab588b200d264c0eb3564690af
Cr-Commit-Position: refs/heads/master@{#33527}

[alph, 2016-01-25 22:08:38]

alph@chromium.org changed reviewers:
+ bmeurer@chromium.org, caseq@chromium.org

[alph, 2016-01-25 22:08:38]

ptal

[alph, 2016-01-25 22:16:06]

alph@chromium.org changed reviewers:
+ yurys@chromium.org

[yurys, 2016-01-25 23:40:24]

lgtm

[ofrobots, 2016-01-26 02:08:38]

On 2016/01/25 23:40:24, yurys wrote:
> lgtm

Just curious about the motivation here. Injecting too samples manually might
skew the sample distribution and make the CpuProfile no longer representative.
How would this be used typically?

[alph, 2016-01-26 02:21:04]

On 2016/01/26 02:08:38, ofrobots wrote:
> On 2016/01/25 23:40:24, yurys wrote:
> > lgtm
> 
> Just curious about the motivation here. Injecting too samples manually might
> skew the sample distribution and make the CpuProfile no longer representative.
> How would this be used typically?

Yes, this is a known tradeoff.
We need this API to attribute some events with stack traces. The user should
understand that injecting samples on irregular basis would affect aggregated
stats.
On the other hand, samples are attributed with timestamps, so DevTools use them
to calculate weights of the call frames.

[alph, 2016-01-26 02:24:09]

On 2016/01/26 02:21:04, alph wrote:
> On 2016/01/26 02:08:38, ofrobots wrote:
> > On 2016/01/25 23:40:24, yurys wrote:
> > > lgtm
> > 
> > Just curious about the motivation here. Injecting too samples manually might
> > skew the sample distribution and make the CpuProfile no longer
representative.
> > How would this be used typically?
> 
> Yes, this is a known tradeoff.
> We need this API to attribute some events with stack traces. The user should
> understand that injecting samples on irregular basis would affect aggregated
> stats.
> On the other hand, samples are attributed with timestamps, so DevTools use
them
> to calculate weights of the call frames.

Oh, just thought that I can make the explicit samples do not add to the stats!
I'll do that. Thanks.

Btw the chromium part is at https://codereview.chromium.org/1624783002/

[Benedikt Meurer, 2016-01-26 10:03:25]

bmeurer@chromium.org changed reviewers:
+ jochen@chromium.org

[Benedikt Meurer, 2016-01-26 10:03:25]

bmeurer@chromium.org changed required reviewers:
+ jochen@chromium.org

[Benedikt Meurer, 2016-01-26 10:03:26]

Adding jochen for API change.

As far as I can tell this is LGTM from my side.

[jochen (gone - plz use gerrit), 2016-01-26 10:14:36]

lgtm

[alph, 2016-01-26 19:46:43]

The CQ bit was checked by alph@chromium.org

[alph, 2016-01-26 19:46:44]

The patchset sent to the CQ was uploaded after l-g-t-m from
bmeurer@chromium.org, jochen@chromium.org, yurys@chromium.org
Link to the patchset: https://codereview.chromium.org/1631043002/#ps40001
(title: "Updating the API function comment.")

[commit-bot: I haz the power, 2016-01-26 19:46:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1631043002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1631043002/40001

[commit-bot: I haz the power, 2016-01-26 19:50:12]

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

[commit-bot: I haz the power, 2016-01-26 19:50:13]

Try jobs failed on following builders:
  v8_linux_arm_rel on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_linux_arm_rel/builds/12878)
  v8_linux_mips64el_compile_rel on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_linux_mips64el_compile_r...)

[alph, 2016-01-26 20:16:18]

The CQ bit was checked by alph@chromium.org

[alph, 2016-01-26 20:16:18]

The patchset sent to the CQ was uploaded after l-g-t-m from
bmeurer@chromium.org, jochen@chromium.org, yurys@chromium.org
Link to the patchset: https://codereview.chromium.org/1631043002/#ps60001
(title: "Fix tests.")

[commit-bot: I haz the power, 2016-01-26 20:16:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1631043002/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1631043002/60001

[commit-bot: I haz the power, 2016-01-26 20:47:29]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2016-01-26 20:48:41]

Description was changed from

==========
Add CollectSample API function to CpuProfiler

It allows embedder to inject a stack sample on demand.

BUG=chromium:579191
LOG=N
==========

to

==========
Add CollectSample API function to CpuProfiler

It allows embedder to inject a stack sample on demand.

BUG=chromium:579191
LOG=N

Committed: https://crrev.com/7068caf5fd614bab588b200d264c0eb3564690af
Cr-Commit-Position: refs/heads/master@{#33527}
==========

[commit-bot: I haz the power, 2016-01-26 20:48:47]

Patchset 4 (id:??) landed as
https://crrev.com/7068caf5fd614bab588b200d264c0eb3564690af
Cr-Commit-Position: refs/heads/master@{#33527}