Ask the GLSurface for the real service ID of the backbuffer.
Ask the GLSurface for the real service ID of the backbuffer.

The real FBO ID of the backbuffer may not be 0 (on OSX and Linux Aura). It's a mistake to assume so.

BUG=none
TEST=none


Review URL: http://codereview.chromium.org/9226018

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@118518 0039d316-1c4b-4281-b951-d872f2087c98

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