code: public boolean showOverflowMenu() {
          if (mReserveOverflow && !isOverflowMenuShowing() && mMenu != null && mMenuView != null &&
                  mPostedOpenRunnable == null && !mMenu.getNonActionItems().isEmpty()) {
              OverflowPopup popup = new OverflowPopup(mContext, mMenu, mOverflowButton, true);
              mPostedOpenRunnable = new OpenOverflowRunnable(popup);
              // Post this for later; we might still need a layout for the anchor to be right.
              ((View) mMenuView).post(mPostedOpenRunnable);
  
              // ActionMenuPresenter uses null as a callback argument here
              // to indicate overflow is opening.
              super.onSubMenuSelected(null);
  
              return true;
          }
          return false;
      }
docs: Display the overflow menu if one is present.
  @return true if the overflow menu was shown, false otherwise.