@Override
    @WorkerThread
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
            String sortOrder) {
        if (!blockUntilFileReady(uri)) return null;
        return super.query(uri, projection, selection, selectionArgs, sortOrder);
    }
Grant the read permission to a list of {@link Uri} sent through a {@link Intent}.
@param intent The sending Intent which holds a list of Uri.
@param uris A list of Uri generated by generateUri(Context, Bitmap, String, int,
            List<String>).
@param context The context requests to grant the permission.
customtabs/src/android/support/customtabs/browseractions/BrowserServiceFileProvider.java