WebGLCompat: Add test for ANGLE_instanced_arrays Also adds a test for an integer overflow in DrawArrays validation. BUG=602737 Change-Id: I71c5bd155cf919964f46e2b0b48267253cab91eb Reviewed-on: https://chromium-review.googlesource.com/716841 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>