xform saveLayer() backdrop

Just noticed this TODO is easy now.  This doesn't seem to change any
GMs, and definitely isn't used by Chrome or Android... this is just for
completeness.

It's also definitely correct to unfurl pictures.

Change-Id: Ida6e43788d1de7a9452dad47aea8a5fbe41a1f46
Reviewed-on: https://skia-review.googlesource.com/14276
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Matt Sarett <msarett@google.com>
3 files changed