Expose global state variables for sampling tracing to WebKit

Expose global state variables for sampling tracing to WebKit

We are implementing TRACE_EVENT macros for sampling profiling. It works in the following mechanism:

- Chromium defines global state variables for sampling profiling. (i.e. g_trace_state0, g_trace_state1, g_trace_state2 in trace_event.h)

- WebKit gets the addresses of the global state variables at the initialization step. (i.e. EventTracer::initialize())

- WebKit updates the global states by using TRACE_EVENT_SAMPLING_STATE() macros every time WebKit changes its state. (e.g. DOM attribute getters/setters/methods)

- A sampling thread running in Chrome reads the global states periodically and visualizes the profiling results into about://tracing.

In this issue, we make a Chromium side change to implement a WebKit API to get the addresses of the global states.

The WebKit patch is here: https://bugs.webkit.org/show_bug.cgi?id=110932

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=186162

[haraken, 2013-02-27 02:35:07]

nduca, scottmg: Would you take a look before a formal review?

The WebKit side patch is here: https://bugs.webkit.org/show_bug.cgi?id=110932

[abarth-chromium, 2013-02-27 02:58:00]

https://codereview.chromium.org/12316146/diff/2001/webkit/glue/webkitplatform...
File webkit/glue/webkitplatformsupport_impl.cc (right):

https://codereview.chromium.org/12316146/diff/2001/webkit/glue/webkitplatform...
webkit/glue/webkitplatformsupport_impl.cc:457: switch(thread_bucket) {
Is this really better than a branch +
TRACE_EVENT_API_THREAD_BUCKET(thread_bucket)

[haraken, 2013-02-27 03:29:55]

https://codereview.chromium.org/12316146/diff/2001/webkit/glue/webkitplatform...
File webkit/glue/webkitplatformsupport_impl.cc (right):

https://codereview.chromium.org/12316146/diff/2001/webkit/glue/webkitplatform...
webkit/glue/webkitplatformsupport_impl.cc:457: switch(thread_bucket) {
On 2013/02/27 02:58:00, abarth wrote:
> Is this really better than a branch +
> TRACE_EVENT_API_THREAD_BUCKET(thread_bucket)

I cannot use it because it results in 'g_trace_statethread_bucket', not
'g_trace_state0'...

(This method is called only three times at the initialization step, so the
performance wouldn't be a problem.)

[scottmg, 2013-03-04 23:33:40]

lgtm

[haraken, 2013-03-04 23:41:19]

On 2013/03/04 23:33:40, scottmg wrote:
> lgtm

Thanks!

brettw: Would you take a look as an OWNER?

[brettw, 2013-03-05 00:45:14]

LGTM rubberstamp

[commit-bot: I haz the power, 2013-03-05 09:34:35]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/haraken@chromium.org/12316146/2001

[commit-bot: I haz the power, 2013-03-05 09:56:16]

Sorry for I got bad news for ya.
Compile failed with a clobber build on android_clang_dbg.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=android_cl...
Your code is likely broken or HEAD is junk. Please ensure your
code is not broken then alert the build sheriffs.
Look at the try server FAQ for more details.

[commit-bot: I haz the power, 2013-03-05 10:27:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/haraken@chromium.org/12316146/10003

[commit-bot: I haz the power, 2013-03-05 12:38:29]

Change committed as 186162