[mdv] Avoid observing placeholder arrays in TemplateIterator

pkg/mdv/test/template_element_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library template_element_test;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:html';
 import 'dart:math' as math;
@@ skipping 1350 matching lines @@
 
     m.add(toSymbols({ 'foo': 'baz' }));
     recursivelySetTemplateModel(div, m);
     performMicrotaskCheckpoint();
 
     expect(div.nodes.length, 5);
     expect(div.nodes[1].text, 'bar');
     expect(div.nodes[3].text, 'baz');
   });
 
+  observeTest('Template - Same Contents, Different Array has no effect', () {
+    if (!MutationObserver.supported) return;
+
+    var div = createTestHtml('<template repeat>{{ foo }}</template>');
+
+    var m = toSymbols([{ 'foo': 'bar' }, { 'foo': 'bat'}]);
+    recursivelySetTemplateModel(div, m);
+    performMicrotaskCheckpoint();
+
+    var observer = new MutationObserver((records, _) {});
+    observer.observe(div, childList: true);
+
+    var template = div.firstChild;
+    template.bind('repeat', toObservable(m.toList()), '');
+    performMicrotaskCheckpoint();
+    var records = observer.takeRecords();
+    expect(records.length, 0);
+  });
+
   observeTest('ChangeFromBindToRepeat', () {
     var div = createTestHtml(
         '<template bind="{{a}}">'
           '{{ length }}'
         '</template>');
     var template = div.nodes.first;
 
     // Note: this test data is a little different from the JS version, because
     // we allow binding to the "length" field of the Map in preference to
     // binding keys.
@@ skipping 320 matching lines @@
       k = k is String ? sym(k) : _deepToSymbol(k);
       result[k] = _deepToSymbol(v);
     });
     return result;
   }
   if (value is Iterable) {
     return value.map(_deepToSymbol).toList();
   }
   return value;
 }