[mdv] Avoid observing placeholder arrays in TemplateIterator

pkg/mdv/lib/src/input_bindings.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.
 
 part of mdv;
 
 abstract class _InputBinding {
   // InputElement or SelectElement
   final element;
   PathObserver binding;
@@ skipping 136 matching lines @@
     }
 
     // The binding may wish to bind to an <option> which has not yet been
     // produced by a child <template>. Furthermore, we may need to wait for
     // <optgroup> iterating and then for <option>.
     //
     // Unlike the JavaScript MDV, we don't have a special "Object.observe" event
     // loop to schedule on. (See the the "ensureScheduled" function:
     // https://github.com/Polymer/mdv/commit/9a51ad7ed74a292bf71662cea28acbd151ff65c8)
     //
     // Instead we use runAsync. Each <template repeat> needs a delay of 3:

[justinfagnani, 2013/07/24 00:42:55]

3 -> 2?

[Jennifer Messerly, 2013/07/24 00:52:58]

Done.

     //   * once to happen after the child _TemplateIterator is created
     //   * once to be after _TemplateIterator.inputs CompoundBinding resolve
-    //   * once to be after _TemplateIterator._valueBinding PathObserver fires
     // And then we need to do this delay sequence twice:
     //   * once for OPTGROUP
     //   * once for OPTION.
-    // The resulting 2 * 3 is our maxRetries.
-    var maxRetries = 6;
+    // The resulting 2 * 2 is our maxRetries.
+    var maxRetries = 4;
     delaySetSelectedIndex() {
       if (newValue > element.length && --maxRetries >= 0) {
         runAsync(delaySetSelectedIndex);
       } else {
         element.selectedIndex = newValue;
       }
     }
 
     runAsync(delaySetSelectedIndex);
   }
 
   void updateBinding(e) {
     binding.value = element.selectedIndex;
   }
 
   // TODO(jmesserly,sigmund): I wonder how many bindings typically convert from
   // one type to another (e.g. value-as-number) and whether it is useful to
   // have something like a int/num binding converter (either as a base class or
   // a wrapper).
   static int _toInt(value) {
     if (value is String) return int.parse(value, onError: (_) => null);
     return value is int ? value : null;
   }
 }