Add UMA metric for tracking listeners for blocking touch before page finished loading

Add UMA metric for tracking listeners for blocking touch before page finished loading

In the touch scrolling intervention proposal, rbyers@ proposed that we could treat
all touch event listeners as passive until the load event fires. We are adding metrics
that record when touchstart or first touchmove events are successfully preventDefaulted()
before the load event to measure breakage of event handlers.

BUG=601179
Review-Url: https://codereview.chromium.org/1879233005
Cr-Commit-Position: refs/heads/master@{#390257}
(cherry picked from commit 0e80d7ffdef2a817d66be17a0e9fe68029f6d8d7)

Committed: https://chromium.googlesource.com/chromium/src/+/5a56668d4208b56616f05f8b68097f7ac3aaa702

[lanwei, 2016-04-29 00:14:04]

Description was changed from

==========
Add UMA metric for tracking listeners for blocking touch before page finished
loading

In the touch scrolling intervention proposal, rbyers@ proposed that we could
treat
all touch event listeners as passive until the load event fires. We are adding
metrics
that record when touchstart or first touchmove events are successfully
preventDefaulted()
before the load event to measure breakage of event handlers.

BUG=601179

Review-Url: https://codereview.chromium.org/1879233005
Cr-Commit-Position: refs/heads/master@{#390257}
(cherry picked from commit 0e80d7ffdef2a817d66be17a0e9fe68029f6d8d7)
==========

to

==========
Add UMA metric for tracking listeners for blocking touch before page finished
loading

In the touch scrolling intervention proposal, rbyers@ proposed that we could
treat
all touch event listeners as passive until the load event fires. We are adding
metrics
that record when touchstart or first touchmove events are successfully
preventDefaulted()
before the load event to measure breakage of event handlers.

BUG=601179

Review-Url: https://codereview.chromium.org/1879233005
Cr-Commit-Position: refs/heads/master@{#390257}
(cherry picked from commit 0e80d7ffdef2a817d66be17a0e9fe68029f6d8d7)

Committed:
https://chromium.googlesource.com/chromium/src/+/5a56668d4208b56616f05f8b6809...
==========

[lanwei, 2016-04-29 00:14:05]

Committed patchset #1 (id:1) manually as
5a56668d4208b56616f05f8b68097f7ac3aaa702.