function onMdContentLoad($event, newContentEl) {
          // Toolbar and content must be siblings
          if (newContentEl && element.parent()[0] === newContentEl.parent()[0]) {
            // unhook old content event listener if exists
            if (contentElement) {
              contentElement.off('scroll', debouncedContentScroll);
            }

            contentElement = newContentEl;
            disableScrollShrink = enableScrollShrink();
          }
        }
@param {null} $event $mdContentLoaded always has a null event
@param {JQLite} newContentEl JQLite object containing an md-content