cc: Make sure mask and replica layers get DidBecomeActive signal.
Since we create and rasterize mask and replica layer tiles as well,
we need to ensure that they get the DidBecomeActive signal in order
to ensure the tile priorities of the contained tiles are correct.
(DidBecomeActive switches active and pending priorities and clears
the pending priority). Without this, there are cases where the pending
priority can remain high without any mechanism clearing it.
BUG=400560
R=enne
Review URL: https://codereview.chromium.org/
441863002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287693 0039d316-1c4b-4281-b951-d872f2087c98