copyTextureCHROMIUM should generate INVALID_VALUE when using a NPOT
texture and level not equal to zero, so we should add
validation to catch this case.

BUG=angleproject:2380

Change-Id: I0ea50a981e4d8f10f5913969f6b629617b57aa15
Reviewed-on: https://chromium-review.googlesource.com/951713
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>