Doc here:
https://docs.google.com/document/d/10O_wMEpKgnhCfEQ8L3JckEKvkcclwEwCLtL0nSl7usA/edit#

Should we add another bug for measuring the benefit this intervention would have, or should we consider that part of this bug?

We will also measure its benefit by recording the time between when touch starts and first touch moves handled by blocking listeners which will be treated as passive are dispatched to the renderer and when they’re acked.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0e80d7ffdef2a817d66be17a0e9fe68029f6d8d7

commit 0e80d7ffdef2a817d66be17a0e9fe68029f6d8d7
Author: lanwei <lanwei@chromium.org>
Date: Thu Apr 28 00:36:22 2016

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}

[modify] https://crrev.com/0e80d7ffdef2a817d66be17a0e9fe68029f6d8d7/third_party/WebKit/Source/core/input/EventHandler.cpp
[modify] https://crrev.com/0e80d7ffdef2a817d66be17a0e9fe68029f6d8d7/tools/metrics/histograms/histograms.xml

Your change meets the bar and is auto-approved for M51 (branch: 2704)

Please merge your change to M51 branch 2704 before 5:00 PM PST, tomorrow (Friday), so we can take it in for next week M51 beta release. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5a56668d4208b56616f05f8b68097f7ac3aaa702

commit 5a56668d4208b56616f05f8b68097f7ac3aaa702
Author: lanwei <lanwei@chromium.org>
Date: Fri Apr 29 00:11:36 2016

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)

Review URL: https://codereview.chromium.org/1924083004 .

Cr-Commit-Position: refs/branch-heads/2704@{#300}
Cr-Branched-From: 6e53600def8f60d8c632fadc70d7c1939ccea347-refs/heads/master@{#386251}

[modify] https://crrev.com/5a56668d4208b56616f05f8b68097f7ac3aaa702/third_party/WebKit/Source/core/input/EventHandler.cpp
[modify] https://crrev.com/5a56668d4208b56616f05f8b68097f7ac3aaa702/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/85c792f7387cf9f434057b26976f31ac4305dc23

commit 85c792f7387cf9f434057b26976f31ac4305dc23
Author: lanwei <lanwei@chromium.org>
Date: Tue May 17 19:25:18 2016

Add UMA metric to track the time saved on making events passive before pageload.

In the touch scrolling intervention proposal, we could treat touchstart and the
first touchmove event listeners as passive before the page is fully loaded.

We are adding a metric that records the time we saved on making touch events passive
before pageload.

BUG= 601179 

Review-Url: https://codereview.chromium.org/1983883002
Cr-Commit-Position: refs/heads/master@{#394188}

[modify] https://crrev.com/85c792f7387cf9f434057b26976f31ac4305dc23/third_party/WebKit/Source/core/input/TouchEventManager.cpp
[modify] https://crrev.com/85c792f7387cf9f434057b26976f31ac4305dc23/tools/metrics/histograms/histograms.xml