Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/polymer/src/property_accessor.dart

Index: observatory_pub_packages/polymer/src/property_accessor.dart
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--- observatory_pub_packages/polymer/src/property_accessor.dart	(revision 0)
+++ observatory_pub_packages/polymer/src/property_accessor.dart	(working copy)
@@ -0,0 +1,69 @@
+// 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
+// using this pattern:
+//
+//     class Foo extends PolymerElement {
+//       ...
+//       @published
+//       get foo => readValue(#foo);
+//       set foo(v) { writeValue(#foo, v); }
+//
+// and internally readValue/writeValue use an instance of this type to
+// implement the semantics in createPropertyAccessor.
+class _PropertyAccessor<T> {
+  // Name of the property, in order to properly fire change notification events.
+  final Symbol _name;
+
+  /// The underlying value of the property.
+  T _value;
+
+  // Polymer element that contains this property, where change notifications are
+  // expected to be fired from.
+  final Polymer _target;
+
+  /// Non-null when the property is bound.
+  Bindable bindable;
+
+  _PropertyAccessor(this._name, this._target, this._value);
+
+  /// Updates the underlyling value and fires the expected notifications.
+  void updateValue(T newValue) {
+    var oldValue = _value;
+    _value = _target.notifyPropertyChange(_name, oldValue, newValue);
+    _target.emitPropertyChangeRecord(_name, newValue, oldValue);
+  }
+
+  /// 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]";
+  }
+}