Clean up in preparation for an implementation change. Add missing
annotations. Rename inner lock to be uniquely named. Use the local
map instead of mMap in the commit logic.
Test: m
Test: m cts && cts-tradefed run commandAndExit cts-dev --module CtsContentTestCases -c android.content.cts.SharedPreferencesTest
Change-Id: Id3a798732c83a4aa6487225e2375ade4985852e2