[WIP] Add WebCore.UseCounter UMA to supercede FeatureObserver

Add WebCore.UseCounter UMA to supercede FeatureObserver

[NOT Yet for full review - waiting on discussion for how best to measure PageVisits]

Due to renderer fast shutdown we can't rely on reporting metrics at
Page destruction time, and the PageVisits scaling factor is also wildly
inaccurate.

Refactor the UseCounter code to move the buggy logic for the existing
metrics into a LegacyCounter class, and implement a new set of metrics
under WebCore.UseCounter.

BUG=236262, 597963

[dtapuska, 2016-05-31 01:10:51]

dtapuska@chromium.org changed reviewers:
+ dtapuska@chromium.org

[dtapuska, 2016-05-31 01:10:52]

https://codereview.chromium.org/2023903003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/frame/UseCounter.cpp (right):

https://codereview.chromium.org/2023903003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/frame/UseCounter.cpp:641:
useCounterHistogram().count(PageVisits);
Are you explicitly counting here even though muted count is >0 ? I expect so.
But it could probably use a comment.

https://codereview.chromium.org/2023903003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/frame/UseCounter.h (right):

https://codereview.chromium.org/2023903003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/frame/UseCounter.h:1245: bool
hasRecordedMeasurement(Feature feature) const { return
m_featuresReported.quickGet(feature); }
The semantics of this are changing wrt muted count.

https://codereview.chromium.org/2023903003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/frame/UseCounter.h:1273: bool
hasRecordedMeasurement(Feature) const;
Is this method called anywhere?

https://codereview.chromium.org/2023903003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/frame/UseCounter.h:1274: void
countCSS(CSSPropertyID feature);
Likely using a consistent verbage here is good. Count vs record. It is different
for features vs css.

[Rick Byers, 2016-05-31 16:08:17]

Description was changed from

==========
Add WebCore.UseCounter UMA to supercede FeatureObserver

Due to renderer fast shutdown we can't rely on reporting metrics at
Page destruction time, and the PageVisits scaling factor is also wildly
inaccurate.

Refactor the UseCounter code to move the buggy logic for the existing
metrics into a LegacyCounter class, and implement a new set of metrics
under WebCore.UseCounter.

BUG=236262, 597963
==========

to

==========
Add WebCore.UseCounter UMA to supercede FeatureObserver

[NOT Yet for full review - waiting on discussion for how best to measure
PageVisits]

Due to renderer fast shutdown we can't rely on reporting metrics at
Page destruction time, and the PageVisits scaling factor is also wildly
inaccurate.

Refactor the UseCounter code to move the buggy logic for the existing
metrics into a LegacyCounter class, and implement a new set of metrics
under WebCore.UseCounter.

BUG=236262, 597963
==========

[Rick Byers, 2016-08-29 19:00:30]

Note this CL has been superceded by: https://codereview.chromium.org/2284503002/
and https://codereview.chromium.org/2290733002/