public Builder allowCloseOnMoveLeft(final boolean allowCloseOnMoveLeft) {
            this.allowCloseOnMoveLeft = allowCloseOnMoveLeft;
            return this;
        }
If allowCloseOnMoveLeft is true and the menu item has no parent (i.e. a root item)
then the menu will be closed. Useful when the menu is triggered by move right on
an explorer tree or similar. Default is false.
stroom-core-client-widget/src/main/java/stroom/widget/menu/client/presenter/ShowMenuEvent.java