Make synchronization in DraftCache (way) more granular.
Make synchronization in DraftCache (way) more granular.

It was previously causing the main thread to block when calling
addOnDraftChangedListener until the DB query is done.

Needed for b/5928517

Change-Id: I5d5114badfb08ea8468503381a4b45920346a4cc

bmaupin/android-sms-plus