API cleanups for Notification.

- Calling build() on a Style now goes through the same
  codepath as calling build() on the Builder.
- Documented new constants and unhidden classes.
- Fixed crash in Action.clone().

Bug: 10112103
Bug: 10461196
Change-Id: I08cd94790b538a361ccf8ff3682f6a86a7812b95
2 files changed