Improve JavaDoc on AtomicFile.
Improve JavaDoc on AtomicFile.

Change-Id: I042fa533ea5d4adca8ae6d42dbd8de32adb34cea

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