feat(toolbar-buttons): Add event for notify overwritten toolbar buttons

react/features/toolbox/components/HelpButton.js

@@ -33,8 +33,16 @@ class HelpButton extends AbstractButton<Props, *> {
      * @returns {void}
      */
     _handleClick() {
+        const { _userDocumentationURL, handleClick } = this.props;
+
+        if (handleClick) {
+            handleClick();
+
+            return;
+        }
+
         sendAnalytics(createToolbarEvent('help.pressed'));
-        openURLInBrowser(this.props._userDocumentationURL);
+        openURLInBrowser(_userDocumentationURL);
     }
 }