cc: Make PrepareToDraw return an enum for why it aborts

This is mostly a cosmetic patch to change a boolean into an enum.

BUG=335289

Review URL: https://codereview.chromium.org/131683005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247869 0039d316-1c4b-4281-b951-d872f2087c98
25 files changed