Reorganize barback's source files.

pkg/barback/lib/src/graph/node_status.dart

 // Copyright (c) 2014, 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 barback.node_status;
+library barback.graph.node_status;
 
 /// The status of a node in barback's package graph.
 ///
 /// A node has three possible statuses: [IDLE], [MATERIALIZING], and [RUNNING].
 /// These are ordered from least dirty to most dirty; the [dirtier] and
 /// [dirtiest] functions make use of this ordering.
 class NodeStatus {
   /// The node has finished its work and won't do anything else until external
   /// input causes it to.
   ///
@@ skipping 29 matching lines @@
 
   String toString() => _name;
 
   /// Returns [this] or [other], whichever is dirtier.
   NodeStatus dirtier(NodeStatus other) {
     if (this == RUNNING || other == RUNNING) return RUNNING;
     if (this == MATERIALIZING || other == MATERIALIZING) return MATERIALIZING;
     return IDLE;
   }
 }