Add UMA metric for tracking root level listeners for blocking touch.

Add UMA metric for tracking root level listeners for blocking touch.

Adjust histogram to capture on each phase of targeting the event instead
of the old histogram which targeted only where the event handler was
registered.

BUG=604790
Review-Url: https://codereview.chromium.org/1980113002
Cr-Commit-Position: refs/heads/master@{#394982}
(cherry picked from commit 05f9fdad56cd5018c8fb31f1866b232d7444f796)

Committed: https://chromium.googlesource.com/chromium/src/+/1bc81470610ce15506855900f93f255280a04a1a

[dtapuska, 2016-05-24 20:12:48]

Description was changed from

==========
Add UMA metric for tracking root level listeners for blocking touch.

Adjust histogram to capture on each phase of targeting the event instead
of the old histogram which targeted only where the event handler was
registered.

BUG=604790

Review-Url: https://codereview.chromium.org/1980113002
Cr-Commit-Position: refs/heads/master@{#394982}
(cherry picked from commit 05f9fdad56cd5018c8fb31f1866b232d7444f796)
==========

to

==========
Add UMA metric for tracking root level listeners for blocking touch.

Adjust histogram to capture on each phase of targeting the event instead
of the old histogram which targeted only where the event handler was
registered.

BUG=604790

Review-Url: https://codereview.chromium.org/1980113002
Cr-Commit-Position: refs/heads/master@{#394982}
(cherry picked from commit 05f9fdad56cd5018c8fb31f1866b232d7444f796)

Committed:
https://chromium.googlesource.com/chromium/src/+/1bc81470610ce15506855900f93f...
==========

[dtapuska, 2016-05-24 20:12:50]

Committed patchset #1 (id:1) manually as
1bc81470610ce15506855900f93f255280a04a1a.