Add a usecounter for SMIL elements in the document

Add a usecounter for SMIL elements in the document

The current SVGAnimation usecounter [1] is skewed by Modernizr [2] and
doesn't count the other animation types such as <animateMotion>. This
patch adds a new usecounter for SMIL animation elements that are in
the document. I manually confirmed this does not fire on the
Modernizr test page [3] whereas the old SVGAnimation counter does.

[1] http://www.chromestatus.com/metrics/feature/timeline/popularity/90
[2] https://github.com/Modernizr/Modernizr/blob/v2.8.3/modernizr.js#L832-L835
[3] http://modernizr.github.io/Modernizr/test/

BUG=258298
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179191

[kouhei (in TOK), 2014-07-30 01:05:24]

lgtm

[pdr., 2014-07-30 01:05:55]

The CQ bit was checked by pdr@chromium.org

[commit-bot: I haz the power, 2014-07-30 01:07:08]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pdr@chromium.org/424273003/1

[commit-bot: I haz the power, 2014-07-30 01:59:37]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu_trigger...)

[commit-bot: I haz the power, 2014-07-30 02:46:09]

Change committed as 179191