Minor SharedPreference clean-up.
Minor SharedPreference clean-up.

Make a member final, line up some comments, and also cache the
expected stat size, not just the mtime.

Change-Id: Ifcc37bd3ab99787280e506deb682200a16da512e

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base