WebGLCompatibility: test for vertex OOB caused by indices BUG=602688 Change-Id: I49a1a9b3753159c91058a7754534383fbc8a778e Reviewed-on: https://chromium-review.googlesource.com/713740 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>