Add events in barback to bubble up the dirty bit.

pkg/barback/lib/src/asset_cascade.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_cascade;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:stack_trace/stack_trace.dart';
@@ skipping 85 matching lines @@
     var phases = transformerPhases.toList();
 
     // Each phase writes its outputs as inputs to the next phase after it.
     // Add a phase at the end for the final outputs of the last phase.
     phases.add([]);
 
     Phase nextPhase = null;
     for (var transformers in phases.reversed) {
       nextPhase = new Phase(this, _phases.length, transformers.toList(),
           nextPhase);
+      nextPhase.onDirty.listen((_) {
+        _newChanges = true;
+        _waitForProcess();
+      });
       _phases.insert(0, nextPhase);
     }
   }
 
   /// Gets the asset identified by [id].
   ///
   /// If [id] is for a generated or transformed asset, this will wait until
   /// it has been created and return it. If the asset cannot be found, throws
   /// [AssetNotFoundException].
   Future<Asset> getAssetById(AssetId id) {
@@ skipping 42 matching lines @@
 
     return null;
   }
 
   /// Adds [sources] to the graph's known set of source assets.
   ///
   /// Begins applying any transforms that can consume any of the sources. If a
   /// given source is already known, it is considered modified and all
   /// transforms that use it will be re-applied.
   void updateSources(Iterable<AssetId> sources) {
-    _newChanges = true;
-
     for (var id in sources) {
       var controller = _sourceControllerMap[id];
       if (controller != null) {
         controller.setDirty();
       } else {
         _sourceControllerMap[id] = new AssetNodeController(id);
         _phases.first.addInput(_sourceControllerMap[id].node);
       }
 
       // If this source was already loading, cancel the old load, since it may
       // return out-of-date contents for the asset.
       if (_loadingSources.containsKey(id)) _loadingSources[id].cancel();
 
       _loadingSources[id] =
           new CancelableFuture<Asset>(_graph.provider.getAsset(id));
       _loadingSources[id].whenComplete(() {
         _loadingSources.remove(id);
       }).then((asset) {
         var controller = _sourceControllerMap[id].setAvailable(asset);
       }).catchError((error) {
         reportError(error);
 
         // TODO(nweiz): propagate error information through asset nodes.
         _sourceControllerMap.remove(id).setRemoved();
       });
     }
-
-    _waitForProcess();
   }
 
   /// Removes [removed] from the graph's known set of source assets.
   void removeSources(Iterable<AssetId> removed) {
-    _newChanges = true;
-
     removed.forEach((id) {
       // If the source was being loaded, cancel that load.
       if (_loadingSources.containsKey(id)) _loadingSources.remove(id).cancel();
 
       var controller = _sourceControllerMap.remove(id);
       // Don't choke if an id is double-removed for some reason.
       if (controller != null) controller.setRemoved();
     });
-
-    _waitForProcess();
   }
 
   void reportError(error) {
     _accumulatedErrors.add(error);
     _errorsController.add(error);
   }
 
   /// Starts the build process asynchronously if there is work to be done.
   ///
   /// Returns a future that completes with the background processing is done.
@@ skipping 85 matching lines @@
       msg.write(prefixLines(error.toString()));
       if (stackTrace != null) {
         msg.write("\n\n");
         msg.write("Stack trace:\n");
         msg.write(prefixLines(stackTrace.toString()));
       }
       return msg.toString();
     }).join("\n\n");
   }
 }