@Override
    protected boolean receiveFile(@NonNull CustomTabsSessionToken sessionToken, @NonNull Uri uri,
            int purpose, @Nullable Bundle extras) {
        boolean success = retrieveBitmap(uri);
        if (success) {
            mFileReceivingLatch.countDown();
        }
        return success;
    }
Returns the instance of the Service. Returns null if it hasn't been bound yet.
customtabs/tests/src/android/support/customtabs/TestCustomTabsService.java