Update charted to 0.4.8 and roll

packages/observe/lib/src/bindable.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.bindable;
-
-/// An object that can be data bound.
-// Normally this is used with 'package:template_binding'.
-// TODO(jmesserly): Node.bind polyfill calls this "observable"
-abstract class Bindable {
-  // Dart note: changed setValue to be "set value" and discardChanges() to
-  // be "get value".
-
-  /// Initiates observation and returns the initial value.
-  /// The callback will be called with the updated [value].
-  ///
-  /// Some subtypes may chose to provide additional arguments, such as
-  /// [PathObserver] providing the old value as the second argument.
-  /// However, they must support callbacks with as few as 0 or 1 argument.
-  /// This can be implemented by performing an "is" type test on the callback.
-  open(callback);
-
-  /// Stops future notifications and frees the reference to the callback passed
-  /// to [open], so its memory can be collected even if this Bindable is alive.
-  void close();
-
-  /// Gets the current value of the bindings.
-  /// Note: once the value of a [Bindable] is fetched, the callback passed to
-  /// [open] should not be called again with this new value.
-  /// In other words, any pending change notifications must be discarded.
-  // TODO(jmesserly): I don't like a getter with side effects. Should we just
-  // rename the getter/setter pair to discardChanges/setValue like they are in
-  // JavaScript?
-  get value;
-
-  /// This can be implemented for two-way bindings. By default does nothing.
-  set value(newValue) {}
-
-  /// Deliver changes. Typically this will perform dirty-checking, if any is
-  /// needed.
-  void deliver() {}
-}