Move Android shadow rendering interface to util library.

BUG=skia:6119

Change-Id: I8318cf2758042ffd0c81c5fa74240acbf7bea61f
Reviewed-on: https://skia-review.googlesource.com/6999
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
7 files changed