Safely wrap window.top in frog dom.

client/tests/client/dom/InnerFrameTest.dart

Index: client/tests/client/dom/InnerFrameTest.dart
diff --git a/client/tests/client/dom/InnerFrameTest.dart b/client/tests/client/dom/InnerFrameTest.dart
index 6e2d9cf1ec477af128574d36cf2750cbbaf46271..be0cd2e6971adbb3591b6411f49d63a10d4a26db 100644
--- a/client/tests/client/dom/InnerFrameTest.dart
+++ b/client/tests/client/dom/InnerFrameTest.dart
@@ -8,15 +8,30 @@ main() {
 
     // The child's frame should not be able to access its parent's
     // document.
+
+    // Check window.frameElement.
     try {
       var parentDocument = window.frameElement.ownerDocument;
       var div = parentDocument.createElement("div");
-      div.id = "illegal";
+      div.id = "illegalFrameElement";
       parentDocument.body.appendChild(div);
       Expect.fail('Should not reach here.');
     } catch (NoSuchMethodException e) {
       // Expected.
     }
+
+    // Check window.top.
+    try {
+      final top = window.top;
+      var parentDocument = top.document;
+      var div = parentDocument.createElement("div");
+      div.id = "illegalTop";
+      parentDocument.body.appendChild(div);
+      Expect.fail('Should not reach here.');
+    } catch (var e) {
+      // Expected.
+      // TODO(vsm): Enforce this is a NoSuchMethodException.
+    }
     return;
   }
 
@@ -32,7 +47,14 @@ main() {
     });
 
   test('frameElement', () {
-      var div = document.getElementById('illegal');
+      var div = document.getElementById('illegalFrameElement');
+
+      // Ensure that this parent frame was not modified by its child.
+      Expect.isNull(div);
+    });
+
+  test('top', () {
+      var div = document.getElementById('illegalTop');
 
       // Ensure that this parent frame was not modified by its child.
       Expect.isNull(div);