cc: Fix CHECK failure in PictureLayerImpl::UpdateTilePriorities

The should_update_tile_priorities_ in UpdateTilePriorities my fail and
here's the sequence of events:

* Context loss while layer is invisible, which clears
should_update_tile_priorities_
* CalculateContentsScale is skipped because layer is invisible
* Layer becomes visible in next commit, and active layer SyncTiling
during the commit will fail the check.

Any condition that causes CalculateContentsScale on the layer works as
well.

Internal bug b/11265055

BUG=
TEST=PictureLayerImplTest.SyncTilingAfterReleaseResource

Review URL: https://codereview.chromium.org/38863002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230735 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230735