WebGLCompatibility: add tests for OOB in DrawElements' index buffer Also add a small fix for a WebGL test where DrawElements with a count of 0 should skip OOB checks. BUG=angleproject:1523 BUG=chromium:668223 Change-Id: I67fbe939f6c8b925551b658b6178dbbae982df89 Reviewed-on: https://chromium-review.googlesource.com/435279 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>