Add msaa flag and UI to viewer

BUG=skia:

Change-Id: I0a24d5e6a4271f84ea5c82eb6d9ede9a1e63f86a
Reviewed-on: https://skia-review.googlesource.com/8787
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
17 files changed