Add no-op function for Gerrit.installGwt in PolyGerrit plugins

Change-Id: I99c67914e45c7be799631de6ddb283f8a0938eec

polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js

@@ -14,6 +14,10 @@
 (function(window) {
   'use strict';
 
+  // GWT JSNI uses $wnd to refer to window.
+  // http://www.gwtproject.org/doc/latest/DevGuideCodingBasicsJSNI.html
+  window.$wnd = window;
+
   function Plugin(opt_url) {
     this._url = new URL(opt_url);
     if (this._url.pathname.indexOf('/plugins') !== 0) {
@@ -64,5 +68,9 @@
     callback(new Plugin(src));
   };
 
+  Gerrit.installGwt = function() {
+    // NOOP since PolyGerrit doesn’t support GWT plugins.
+  };
+
   window.Gerrit = Gerrit;
 })(window);