Fix for ANGLE and readpixels.
Fix for ANGLE and readpixels.

TEST=webgl conformance tests pass
BUG=76093 

Review URL: http://codereview.chromium.org/6677024

git-svn-id: http://src.chromium.org/svn/trunk/src@78132 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 1bd75ec22afffab2eb1194b06137822fb404234c
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser