Add OnBeforeTraceLogDisabled notification to EnabledStateObserver

Add OnBeforeTraceLogDisabled notification to EnabledStateObserver

The method can be used to perform last call actions that require
tracing still being enabled.

BUG=406277

[alph, 2014-08-20 15:58:53]

Nat, could you please take a look. Thanks!

[yurys, 2014-08-22 06:15:06]

Pleas file a bug describing the approach with V8 CPU profile written into a
trace event and why this change is necessary.

https://codereview.chromium.org/492823002/diff/1/base/debug/trace_event_impl.h
File base/debug/trace_event_impl.h (right):

https://codereview.chromium.org/492823002/diff/1/base/debug/trace_event_impl....
base/debug/trace_event_impl.h:508: virtual void OnTraceLogDisabling() { }
I'd rather call it OnAboutToDisableTraceLog or something to stress that it is
fired before the log is disabled.

[alph, 2014-08-22 09:58:35]

https://codereview.chromium.org/492823002/diff/1/base/debug/trace_event_impl.h
File base/debug/trace_event_impl.h (right):

https://codereview.chromium.org/492823002/diff/1/base/debug/trace_event_impl....
base/debug/trace_event_impl.h:508: virtual void OnTraceLogDisabling() { }
On 2014/08/22 06:15:06, yurys wrote:
> I'd rather call it OnAboutToDisableTraceLog or something to stress that it is
> fired before the log is disabled.

Done.

[yurys, 2014-08-22 12:29:07]

lgtm

[alph, 2014-08-28 14:02:01]

ping

[dsinclair, 2014-09-02 14:29:22]

lgtm

[dsinclair, 2014-09-04 14:14:46]

On 2014/09/02 14:29:22, dsinclair wrote:
> lgtm

The description is out of date, the method is called OnBeforeTraceLogDisabled.

[alph, 2014-09-04 14:58:52]

On 2014/09/04 14:14:46, dsinclair wrote:
> On 2014/09/02 14:29:22, dsinclair wrote:
> > lgtm
> 
> The description is out of date, the method is called OnBeforeTraceLogDisabled.

Oh, yes. Thanks!

[nduca, 2015-03-13 02:23:20]

i do not really like this approach. i would like to have an explicit add
metadata function, because it is more rational and follows the "say what you
mean" idiom. This is a trick. Please reconsider.

[pfeldman, 2015-03-13 04:42:35]

That's the one that is used to send the v8 samples as a single trace event.
It'll go away once the samples get into tracing the right way.

Should we rename it for now to discourage the use? Otherwise not sure why you
are commenting on a 6 month old code review.

[alph, 2015-03-13 07:01:49]

On 2015/03/13 04:42:35, pfeldman wrote:
> That's the one that is used to send the v8 samples as a single trace event.
> It'll go away once the samples get into tracing the right way.
> 
> Should we rename it for now to discourage the use? Otherwise not sure why you
> are commenting on a 6 month old code review.

It has never been landed. We didn't use it. The profile event injection is done
in frontend.

[pfeldman, 2015-03-13 07:38:47]

Ouch. I was sure it made its way into repo. alph@, we need to make sure samples
are in trace asap.