merge to trunk all changes from 36817 until 37378 under the packages: polymer,

pkg/template_binding/lib/src/element.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 template_binding;
 
 /** Extensions to the [Element] API. */
 class _ElementExtension extends NodeBindExtension {
   _ElementExtension(Element node) : super._(node);
 
   bind(String name, value, {bool oneTime: false}) {
-    _self.unbind(name);
-
     Element node = _node;
 
     if (node is OptionElement && name == 'value') {
       // Note: because <option> can be a semantic template, <option> will be
       // a TemplateBindExtension sometimes. So we need to handle it here.
       node.attributes.remove(name);
 
       if (oneTime) return _updateOption(value);
       _open(value, _updateOption);
     } else {
       bool conditional = name.endsWith('?');
       if (conditional) {
         node.attributes.remove(name);
         name = name.substring(0, name.length - 1);
       }
 
       if (oneTime) return _updateAttribute(_node, name, conditional, value);
 
       _open(value, (x) => _updateAttribute(_node, name, conditional, x));
     }
-    return bindings[name] = value;
+    return _maybeUpdateBindings(name, value);
   }
 
   void _updateOption(newValue) {
     OptionElement node = _node;
     var oldValue = null;
     var selectBinding = null;
     var select = node.parentNode;
     if (select is SelectElement) {
-      var valueBinding = nodeBind(select).bindings['value'];
-      if (valueBinding is _InputBinding) {
-        selectBinding = valueBinding;
-        oldValue = select.value;
+      var bindings = nodeBind(select).bindings;
+      if (bindings != null) {
+        var valueBinding = bindings['value'];
+        if (valueBinding is _InputBinding) {
+          selectBinding = valueBinding;
+          oldValue = select.value;
+        }
       }
     }
 
     node.value = _sanitizeValue(newValue);
 
     if (selectBinding != null && select.value != oldValue) {
       selectBinding.value = select.value;
     }
   }
 }
 
 void _updateAttribute(Element node, String name, bool conditional, value) {
   if (conditional) {
     if (_toBoolean(value)) {
       node.attributes[name] = '';
     } else {
       node.attributes.remove(name);
     }
   } else {
     // TODO(jmesserly): escape value if needed to protect against XSS.
     // See https://github.com/polymer-project/mdv/issues/58
     node.attributes[name] = _sanitizeValue(value);
   }
 }