fix(gesture): check if navigator is defined before accessing userAgent (#11755)

fixes a build error when using `angular/material-tools`

Fixes #11751

Author: Splaktar

src/core/services/gesture/gesture.js

@@ -17,9 +17,12 @@ var lastLabelClickPos = null;
 // Used to attach event listeners once when multiple ng-apps are running.
 var isInitialized = false;
 
-var userAgent = navigator.userAgent || navigator.vendor || window.opera;
-var isIos = userAgent.match(/ipad|iphone|ipod/i);
-var isAndroid = userAgent.match(/android/i);
+// Support material-tools builds.
+if (window.navigator) {
+  var userAgent = window.navigator.userAgent || window.navigator.vendor || window.opera;
+  var isIos = userAgent.match(/ipad|iphone|ipod/i);
+  var isAndroid = userAgent.match(/android/i);
+}
 
 /**
  * @ngdoc module