Add paint flags to viewer GUI.

Overriding bits of the paint was added with keyboard bindings but
without being reflected in the GUI. This adds these flags to the GUI.

Change-Id: I633801fb776248952afe7cbe8857676ef8b57135
Reviewed-on: https://skia-review.googlesource.com/121796
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
3 files changed