Update to polymer js version 0.4.1

pkg/polymer/lib/src/property_accessor.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.
 
 /// Code for property accessors from declaration/properties.js
 part of polymer;
 
 // Dart note: this matches the property defined by createPropertyAccessor in
 // polymer-dev/src/declarations/properties.js. Unlike Javascript, we can't
 // override the original property, so we instead ask users to write properties
@@ skipping 33 matching lines @@
   /// The current value of the property. If the property is bound, reading this
   /// property ensures that the changes are first propagated in order to return
   /// the latest value. Similarly, when setting this property the binding (if
   /// any) will be updated too.
   T get value {
     if (bindable != null) bindable.deliver();
     return _value;
   }
 
   set value(T newValue) {
+    // Dart Note: The js side makes computed properties read only, and bails
+    // out right here for them (ignoreWrites). For us they are automatically
+    // read only unless you define a setter for them, so we left that out.
     if (bindable != null) {
       bindable.value = newValue;
     } else {
       updateValue(newValue);
     }
   }
 
   toString() {
     var name = smoke.symbolToName(_name);
     var hasBinding = bindable == null ? '(no-binding)' : '(with-binding)';
     return "[$runtimeType: $_target.$name: $_value $hasBinding]";
   }
 }