Make Assets know their ID.

pkg/barback/lib/src/asset_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 barback.asset_graph;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'asset.dart';
 import 'asset_id.dart';
 import 'asset_provider.dart';
+import 'asset_set.dart';
 import 'errors.dart';
 import 'change_batch.dart';
 import 'phase.dart';
 import 'transformer.dart';
 
 /// The main build dependency manager.
 ///
 /// For any given input file, it can tell which output files are affected by
 /// it, and vice versa.
 class AssetGraph {
@@ skipping 160 matching lines @@
     // changes are processed in a single batch even when the first one starts
     // the build process.
     return new Future(() {
       if (_sourceChanges == null) return null;
 
       // Take the current batch to ensure it doesn't get added to while we're
       // processing it.
       var changes = _sourceChanges;
       _sourceChanges = null;
 
-      var updated = new Map<AssetId, Asset>();
+      var updated = new AssetSet();
       var futures = [];
       for (var id in changes.updated) {
         // TODO(rnystrom): Catch all errors from provider and route to results.
         futures.add(_provider.getAsset(id).then((asset) {
-          updated[id] = asset;
+          updated.add(asset);
         }).catchError((error) {
           if (error is AssetNotFoundException) {
             // Handle missing asset errors like regular missing assets.
             reportError(error);
           } else {
             // It's an unexpected error, so rethrow it.
             throw error;
           }
         }));
       }
 
       return Future.wait(futures).then((_) {
         _phases.first.updateInputs(updated, changes.removed);
       });
     });
   }
 }
 
 /// Used to report build results back from the asynchronous build process
 /// running in the background.
 class BuildResult {
   /// The error that occurred, or `null` if the result is not an error.
   final error;
 
   /// `true` if this result is for a successful build.
   bool get succeeded => error == null;
 
   BuildResult([this.error]);
 }