Revert 251095 "Revert 250828 "Add a UMA stat to track if the Bro..."

Speculative re-land to see if this causes sync tests failures again.
If it does, then we will know if this is the cause.

> Revert 250828 "Add a UMA stat to track if the Browser blacklist ..."
> 
> Speculative revert for failures here:
> 
> http://build.chromium.org/p/chromium.win/builders/Win7%20Sync%20x64/builds/11201
> 
> > Add a UMA stat to track if the Browser blacklist is Set on the Renderer
> > 
> > This shouldn't be happening, but we got some crash reports suggesting it
> > does. Unable to repo locally so this stat will verify it does occur and
> > then can be used to verify our fixes actually fix it.
> > 
> > BUG=329023
> > 
> > Review URL: https://codereview.chromium.org/140763008
> 
> TBR=csharp@chromium.org
> 
> Review URL: https://codereview.chromium.org/163633005

TBR=asvitkine@chromium.org

Review URL: https://codereview.chromium.org/164833002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251134 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251134
[GCM] Add basic collapse key support for upstream

Messages are collapsed based on app + token as long as they have not
been sent over the wire yet. If messages are resent (because original send
failed for some reason) no collapsing is done at this point in time.

BUG=284553

Review URL: https://codereview.chromium.org/148293002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251135 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251135