@NonNull
        public Builder addMenuItem(@NonNull String label, @NonNull PendingIntent pendingIntent) {
            if (mMenuItems == null) mMenuItems = new ArrayList<>();
            Bundle bundle = new Bundle();
            bundle.putString(KEY_MENU_ITEM_TITLE, label);
            bundle.putParcelable(KEY_PENDING_INTENT, pendingIntent);
            mMenuItems.add(bundle);
            return this;
        }
Adds a menu item.

@param label Menu label.
@param pendingIntent Pending intent delivered when the menu item is clicked.
customtabs/src/android/support/customtabs/CustomTabsIntent.java