cleanup to tools/testing/dart

tools/testing/dart/lib/dependency_graph.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 dependency_graph;
 
 import 'dart:async';
+
 import 'utils.dart';
 
-
 /*
  * [Graph] represents a datastructure for representing an DAG (directed acyclic
  * graph). Each node in the graph is in a given [NodeState] and can have data
  * attachted to it with [Node.userData].
  *
  * It's interface consists basically of these methods:
  *   - newNode: Adds a new node to the graph with the given dependencies and
  *              the given user data. The node is in the [NodeState.Initialized]
  *              state.
  *   - changeState: Changes the state of a node.
@@ skipping 117 matching lines @@
   NodeAddedEvent(this.node);
 }
 
 class StateChangedEvent extends GraphEvent {
   final Node node;
   final NodeState from;
   final NodeState to;
 
   StateChangedEvent(this.node, this.from, this.to);
 }