This will unify the way we call into PackPixels and also cleans u
the code. It required adding a few D3D9-specific formats to the table.

BUG=angleproject:1455

Change-Id: Ic8282f40f52cabdb2925e2bb305c26582284082d
Reviewed-on: https://chromium-review.googlesource.com/365825
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>