Part 1: MessageView
- It's an attempt to get rid of Handlers from Activities, and
reduce the amount of code that runs run a BG thread in them.
- Introduced ResultUiThreadWrapper, which wraps another Controller.Result
and make callbacks get called on the UI thread.
- It'll make the logic in ControllerResults cleaner and more straightforward.
- ResultUiThreadWrapper isn't too memory efficient because it allocates a
Runnable even if the wrappee's target method is empty.
However these callbacks don't get called often, and optimizing it would
make code more complicated, so I don't think it's worth optimizing.
- Now we can assume all the methods in activities except
AsyncTask.doInBackground runs on the UI thread, with some special exceptions
like MediaScannerNotifier.
In my previous abandoned change, I named methods that can run on BG threads
'*OnUiThread', but now there's no need to do that.
This also means we can minimize the use of synchronizations.
Change-Id: Ia6d9d2a266ebf5a4b23d712e9eaea3272adbd2a6
7e24c6c6f9