Changed WebGL Validation to return INVALID_OPERATION any time an
indexed draw call is made without a bound ELEMENT_ARRAY_BUFFER. Spec
was changed to no longer require count > 0 in order to cause error.
Make same spec change to GL_ANGLE_client_arrays extension.

BUG:angleproject:2639
Change-Id: I23963f357119d081890aa5387b2863e1d42b92a5
Reviewed-on: https://chromium-review.googlesource.com/1093984
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>