Break BackRenderbuffer dependency on the decoder.

BUG=

Review URL: https://codereview.chromium.org/26320002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227847 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227847
Clang update script: simplify code for file clobbering

This makes the code a lot simpler.

BUG=none

Review URL: https://codereview.chromium.org/26736002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227848 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227848