Implemented failIfMajorPerformanceCaveat WebGL context creation attribute.

Currently only fails if using swiftshader.

BUG=319965
R=kbr@chromium.org, piman@chromium.org, zmo@chromium.org

Review URL: https://codereview.chromium.org/79123004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237661 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237661