Limit each parse to batches of a few words, to keep the UI thread
responsive.
Possible optimizations for the future:
- SpellCheck in a thread, but that requires some locking mecanism
- Only spell check what is visible on screen. Will require additional
spans to tag the pieces of text.
This is a cherry pick of 145656 into ICS-MR1
Patch Set 2: Make the Runnable shared and stop it when detached.
Change-Id: Ibf8e98274bda84b7176aac181ff267fc1f1fa4cb
be5f49fb6e