Enable cross-package transforms to see new transformers in other packages.

pkg/barback/lib/src/phase_output.dart

Index: pkg/barback/lib/src/phase_output.dart
diff --git a/pkg/barback/lib/src/phase_output.dart b/pkg/barback/lib/src/phase_output.dart
index ae309d9820eba63990cd6e77601aabc457d5a267..ccfc15971703204f59e081e0aec99c8fa83336f7 100644
--- a/pkg/barback/lib/src/phase_output.dart
+++ b/pkg/barback/lib/src/phase_output.dart
@@ -28,7 +28,7 @@ class PhaseOutput {
 
   /// The asset node for this output.
   AssetNode get output => _outputController.node;
-  final AssetNodeController _outputController;
+  AssetNodeController _outputController;
 
   /// The assets for this output.
   ///
@@ -59,6 +59,16 @@ class PhaseOutput {
     _watchAsset(node);
   }
 
+  /// Removes all existing listeners on [output] without actually closing
+  /// [this].
+  ///
+  /// This marks [output] as removed, but immediately replaces it with a new
+  /// [AssetNode] in the same state as the old output.

[Bob Nystrom, 2013/08/22 19:34:19]

A bit of motivation here would help.

+  void removeListeners() {
+    _outputController.setRemoved();
+    _outputController = new AssetNodeController.from(_assets.first);
+  }
+
   /// Watches [node] for state changes and adjusts [_assets] and [output]
   /// appropriately when they occur.
   void _watchAsset(AssetNode node) {