Verify YUVA channel information and add premultiplied alpha

Bug: skia:7903
Change-Id: Ia5394192febd1ffb6f2dcf700fc551407ceb80c1
Reviewed-on: https://skia-review.googlesource.com/c/170265
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
7 files changed