Enable MtpDocumentsProvider by default.
Enable MtpDocumentsProvider by default.

BUG=20274999

Change-Id: I35941df66fea4ab703f8f1de3c69b6f4dd2be9a0

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