When a texture storage is deleted, it copies its mip levels back into
images and marks them clean.  Marking the images dirty before deleting the
texture storage would have no effect.

BUG=705865

Change-Id: Ib4c0fc9bea1236fc31963d1b7db814785bc54abc
Reviewed-on: https://chromium-review.googlesource.com/486107
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>