CL is prepared here: https://chromiumcodereview.appspot.com/2864113002/

Is this still needed given the UMA UI allows us to visualize the metric we want to track via formulas?

https://uma.googleplex.com/p/chrome/timeline_v2/?sid=48f3a236a3c4e746f555c564881bc26f

xhwang@, I realized we could do this only after our chat this morning.

We already have Permissions.Action.ProtectedMedia on Android, which is consistent with all other permissions. I'd like to enable our ChromeOS UMA to use that as well.

Also, currently we don't know how many users actually dismissed the prompt, which will be available in Permissions.Action.ProtectedMedia.

It's a trivial CL, so I feel it's still worth it.

Makes sense - completely agree that knowing how many users are dismissing the prompt is a valuable signal.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/caeedfbcb7eb8a9a9a1a262c385af7c49045a864

commit caeedfbcb7eb8a9a9a1a262c385af7c49045a864
Author: xhwang <xhwang@chromium.org>
Date: Tue May 09 03:44:59 2017

media: Add Permissions.Action.ProtectedMedia UMA on ChromeOS

BUG= 719111 
TEST=Maually tested

Review-Url: https://codereview.chromium.org/2864113002
Cr-Commit-Position: refs/heads/master@{#470160}

[modify] https://crrev.com/caeedfbcb7eb8a9a9a1a262c385af7c49045a864/chrome/browser/media/protected_media_identifier_permission_context.cc