MediaExtractor: Allow reading of app data files.

Needed to allow lower power Play Music of downloaded files.

    05-24 10:12:49.331 24025 24025 W generic : type=1400
          audit(0.0:1259): avc: denied { read } for
          path="/data/data/com.google.android.music/files/music/925.mp3"
          dev="sda35" ino=2179256 scontext=u:r:mediaextractor:s0
          tcontext=u:object_r:app_data_file:s0:c512,c768 tclass=file
          permissive=0

Test: Play Music
Bug: 62059834

Change-Id: I97bdb1d175dba8f7a8ec6cd9084323cfcd3660bd

public/mediaextractor.te

@@ -22,6 +22,7 @@ crash_dump_fallback(mediaextractor)
 
 # allow mediaextractor read permissions for file sources
 allow mediaextractor media_rw_data_file:file { getattr read };
+allow mediaextractor app_data_file:file { getattr read };
 
 # Read resources from open apk files passed over Binder
 allow mediaextractor apk_data_file:file { read getattr };