those checked during ReadPixels. These changes are needed to avoid
having ANGLE assert in debug builds when running WebGL test cases
which provoke a GPU reset.

BUG=none
TEST=slow-shader-example and lots-of-polys-example in WebGL test suite
Review URL: http://codereview.appspot.com/4684042

git-svn-id: https://angleproject.googlecode.com/svn/trunk@703 736b8ea6-26fd-11df-bfd4-992fa37f6226