Also allow apps to read the contents of mounted OBBs.
See AOSP Change-Id: I66df236eade3ca25a10749dd43d173ff4628cfad
and Change-Id: I49b722b24c1c7d9ab084ebee7c1e349d8d660ffa
Change-Id: I757a2a8831c69d41c0496025a39eaf79ceb0e65f
Assets such as composed icons and ringtones need to be accessed
by apps. This patch adds the policy needed to facilitate this.
Change-Id: If47920b2cc5dbafe8d71a621782bb4a3351bd68c