minimize an unnecessary critical section on the UI thread

Adapter.getItemId was blocking on the cursor-advancing lock in
ThreadSafeCursorWrapper, occasionally causing the UI thread to block on
the background CacheLoaderTask.

Changed getItemId to use the Conversation cache when feasible.

Bug: 9032162
Change-Id: I19f00ceefeb52e580b1e3311c6625a4f034f0402
2 files changed