The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6126ee74cd5a98a55b6a1d3991fb0018ca425136

commit 6126ee74cd5a98a55b6a1d3991fb0018ca425136
Author: zqzhang <zqzhang@chromium.org>
Date: Fri Apr 22 13:50:43 2016

[MediaNotification] Add UMA to record user clicking media notifications

This CL adds UMA to record how often the user clicks media notifications
to go back to Chrome.

BUG= 605156 

Review URL: https://codereview.chromium.org/1909483003

Cr-Commit-Position: refs/heads/master@{#389090}

[modify] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/chrome/android/java/src/org/chromium/chrome/browser/document/ChromeLauncherActivity.java
[modify] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/chrome/android/java/src/org/chromium/chrome/browser/media/remote/CastNotificationControl.java
[modify] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/chrome/android/java/src/org/chromium/chrome/browser/media/remote/ExpandedControllerActivity.java
[modify] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/chrome/android/java/src/org/chromium/chrome/browser/media/router/cast/CastSessionImpl.java
[modify] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaNotificationManager.java
[modify] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/chrome/android/java/src/org/chromium/chrome/browser/media/ui/MediaSessionTabHelper.java
[modify] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/chrome/android/java/src/org/chromium/chrome/browser/metrics/LaunchMetrics.java
[add] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/chrome/android/java/src/org/chromium/chrome/browser/metrics/MediaNotificationUma.java
[modify] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/chrome/android/java_sources.gni
[modify] https://crrev.com/6126ee74cd5a98a55b6a1d3991fb0018ca425136/tools/metrics/histograms/histograms.xml