Move validation from IndexDataManager to the API. This validates all necessary buffer sizes for element array buffers in the validation layer, before we start the draw. BUG=angle:571 Change-Id: I602744ca1ea493e9f0f7e1ccbeb85fc4ae5c9f5a Reviewed-on: https://chromium-review.googlesource.com/210648 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>