Delay binding the VAO in VertexArrayGL::syncDrawState until we actually
need to make glVertexAttrib calls.

BUG=angleproject:2188

Change-Id: Ib7d22d641c9f19c639ba8c596bff6bc7de952e7f
Reviewed-on: https://chromium-review.googlesource.com/919503Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Luc Ferron <lucferron@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>