@Override
    @WorkerThread
    public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
        if (!blockUntilFileReady(uri)) {
            throw new FileNotFoundException("File open is interrupted");
        }
        return super.openFile(uri, mode);
    }
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