[GCM] Add per-app limits to persistent store

Per app limits are enforced at the time an attempt to add a message to the
persistent store is made. By default the limit is 20 messages per app, but
future patches may introduce configurable limits.

BUG=284553

Review URL: https://codereview.chromium.org/99073010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244589 0039d316-1c4b-4281-b951-d872f2087c98
Remove VideoRenderer::NaturalSizeChangedCB.

Instead WebMediaPlayerImpl detects frame size changes and bypasses the previous plumbing through Pipeline.

BUG=319000

Review URL: https://codereview.chromium.org/113233004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244590 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244590