This patch changes arguments for MultiDrawElements and
MultiDrawElementsInstanced from from GLsizei *offsets to
const* GLvoid* indices.

Bug: chromium:890539

Change-Id: I2124cf2daeaa6af0f889f3c46aa2b8c77be200a6
Reviewed-on: https://chromium-review.googlesource.com/c/1352591Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>