Replacing commitRect with commitRegion, which takes generic
parameter types, will allow us to call it directly from the
base class TextureD3D. This will be useful in subsequent
patches that introduce the SubData performance workaround.

BUG=angle:729

Change-Id: I37bf12f847b43f7c961b403321de19f547258b01
Reviewed-on: https://chromium-review.googlesource.com/220274Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>