GitLab

We currently represent surface ids as just an int, but may want to move
to a richer data structure in the future. Identifiers that are ints are also
pretty easy to confuse with other ints.

R=piman@chromium.org

Review URL: https://codereview.chromium.org/331533002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276923 0039d316-1c4b-4281-b951-d872f2087c98