Add cr.isIos for features that only apply on iOS

ui/webui/resources/js/cr.js

Index: ui/webui/resources/js/cr.js
diff --git a/ui/webui/resources/js/cr.js b/ui/webui/resources/js/cr.js
index 090cfd94f7d7067fbfeca0ed4e0a44c97294d7a9..ea17af8429a9ae6ce07d67e571ba9c6a293e7592 100644
--- a/ui/webui/resources/js/cr.js
+++ b/ui/webui/resources/js/cr.js
@@ -475,6 +475,11 @@ var cr = cr || function() {
     /** 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);
+    },
   };
 }();