Add a gpu driver bug workaround to count in all varyings in packing check.

This is to workaround a Mesa driver bug.

BUG=333885
TEST=gpu_unittests, test as mentioned in the bug report
R=bajones@chromium.org, kbr@chromium.org

Review URL: https://codereview.chromium.org/153173002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249547 0039d316-1c4b-4281-b951-d872f2087c98
7 files changed