Allow constrained and unconstrained picture-images

BUG=skia:

Change-Id: Id9b7b2c82c634fec50f9a57f4b59ce0c02e0706a
Reviewed-on: https://skia-review.googlesource.com/6818
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
3 files changed