Add ShadowUtils sample.

Also enables mouse support in Viewer.

Change-Id: Iaed08d42a64f591f0cd9b24684b3aee43404ed94
Reviewed-on: https://skia-review.googlesource.com/15313
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
5 files changed