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

pkg/observe/lib/src/path_observer.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 observe.src.path_observer;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:math' show min;
 
@@ skipping 23 matching lines @@
   /// See [open] and [value].
   PathObserver(Object object, [path])
       : _object = object,
         _path = path is PropertyPath ? path : new PropertyPath(path);
 
   bool get _isClosed => _path == null;
 
   /// Sets the value at this path.
   void set value(Object newValue) {
     if (_path != null) _path.setValueFrom(_object, newValue);
+    _discardChanges();
   }
 
   int get _reportArgumentCount => 2;
 
   /// Initiates observation and returns the initial value.
   /// The callback will be passed the updated [value], and may optionally be
   /// declared to take a second argument, which will contain the previous value.
   open(callback) => super.open(callback);
 
   void _connect() {
@@ skipping 370 matching lines @@
 
     if (path is! PropertyPath) path = new PropertyPath(path);
     _observed..add(object)..add(path);
   }
 
   void addObserver(Bindable observer) {
     if (_isOpen || _isClosed) {
       throw new StateError('Cannot add observers once started.');
     }
 
-    observer.open(_deliver);
+    observer.open((_) => deliver());
     _observed..add(_observerSentinel)..add(observer);
   }
 
   void _iterateObjects(void observe(obj)) {
     for (var i = 0; i < _observed.length; i += 2) {
       var object = _observed[i];
       if (!identical(object, _observerSentinel)) {
         (_observed[i + 1] as PropertyPath)._iterateObjects(object, observe);
       }
     }
@@ skipping 80 matching lines @@
           'fewer arguments');
     }
 
     _notifyCallback = callback;
     _notifyArgumentCount = min(_reportArgumentCount, smoke.maxArgs(callback));
 
     _connect();
     return _value;
   }
 
-  get value {
-    _check(skipChanges: true);
-    return _value;
-  }
+  get value => _discardChanges();
 
   void close() {
     if (!_isOpen) return;
 
     _disconnect();
     _value = null;
     _notifyCallback = null;
   }
 
-  void _deliver(_) {
-    if (_isOpen) _dirtyCheck();
+  _discardChanges() {
+    _check(skipChanges: true);
+    return _value;
   }
 
+  bool deliver() => _isOpen ? _dirtyCheck() : false;
+
   bool _dirtyCheck() {
     var cycles = 0;
     while (cycles < _MAX_DIRTY_CHECK_CYCLES && _check()) {
       cycles++;
     }
     return cycles > 0;
   }
 
   void _report(newValue, oldValue, [extraArg]) {
     try {
@@ skipping 108 matching lines @@
     for (var observer in _observers.values.toList(growable: false)) {
       if (observer._isOpen) observer._check();
     }
 
     _resetNeeded = true;
     scheduleMicrotask(reset);
   }
 }
 
 const int _MAX_DIRTY_CHECK_CYCLES = 1000;