This hides the logic for manipulating the current layout and barriers
into the image helper. This will make it easier to implement implicit
pipeline barriers. It allows us to remove the updateLayout() hack.

Bug: angleproject:2828
Change-Id: I3e59872e66064e6b105c1f398b4212fb3a6be1a7
Reviewed-on: https://chromium-review.googlesource.com/1255506
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>