Add cr.isIos for features that only apply on iOS

ui/webui/resources/js/cr.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * The global object.
  * @type {!Object}
  * @const
  */
 var global = this;
@@ skipping 457 matching lines @@
     },
 
     /** Whether this is on vanilla Linux (not chromeOS). */
     get isLinux() {
       return /Linux/.test(navigator.userAgent);
     },
 
     /** Whether this is on Android. */
     get isAndroid() {
       return /Android/.test(navigator.userAgent);
-    }
+    },
+
+    /** Whether this is on iOS. */
+    get isIos() {
+      return /iPad|iPhone|iPod/.test(navigator.userAgent);
+    },
   };
 }();