Fixes http://b/issue?id=1905863
This is needed to address two security issues with global search:
http://b/issue?id=1871088 (Apps can read content providers through GlobalSearch)
http://b/issue?id=1819627 (Apps can use GlobalSearch to launch arbirtrary intents)
This also fixes http://b/issue?id=1693153 (SearchManager.OnDismissListener
never gets called)
To fix the security issues, GlobalSearch also needs to require
a non-app permission to access its content provider and launch intents.
This allows content providers to use in-memory data to implement
ContentProvider.openAssetFile(), instead of just normal files
and sockets as before.
To test cross-process use of AssetFileDescriptors for MemoryFiles,
a test content provider and a client for it are added to
AndroidTests.
Fixes http://b/issue?id=1871731
