code: public void register(final GVRSceneObject sceneObject, final Focusable focusable) {
          Log.d(Log.SUBSYSTEM.FOCUS, TAG, "register sceneObject %s , focusable = %s",
                  sceneObject.getName(), focusable);
          mFocusableMap.put(sceneObject, new WeakReference<>(focusable));
      }
docs: Registers the {@link Focusable} to manage focus for the particular scene object.
  The focus manager will not hold strong references to the sceneObject and the focusable.
  @param sceneObject
  @param focusable