public static int getMaxToolbarItems() {
        return MAX_TOOLBAR_ITEMS;
    }
@return The maximum number of allowed toolbar items for
{@link CustomTabsIntent.Builder#addToolbarItem(int, Bitmap, String, PendingIntent)} and
{@link CustomTabsIntent#EXTRA_TOOLBAR_ITEMS}.
customtabs/src/android/support/customtabs/CustomTabsIntent.java