Make Phase.getInput in barback play nicely with the push model.

pkg/barback/lib/src/transform_node.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.transform_node;
 
 import 'dart:async';
 
 import 'package:source_maps/span.dart';
 
@@ skipping 211 matching lines @@
   ///
   /// If an input with that ID cannot be found, throws an
   /// [AssetNotFoundException].
   Future<Asset> getInput(AssetId id) {
     return phase.getInput(id).then((node) {
       // Throw if the input isn't found. This ensures the transformer's apply
       // is exited. We'll then catch this and report it through the proper
       // results stream.
       if (node == null) throw new MissingInputException(info, id);
 
-      // If the asset node is found, wait until its contents are actually
-      // available before we return them.
-      return node.whenAvailable((asset) {
-        _inputSubscriptions.putIfAbsent(node.id,
-            () => node.onStateChange.listen((_) => _dirty()));
+      _inputSubscriptions.putIfAbsent(node.id,
+          () => node.onStateChange.listen((_) => _dirty()));
 
-        return asset;
-      }).catchError((error) {
-        if (error is! AssetNotFoundException || error.id != id) throw error;
-        // If the node was removed before it could be loaded, treat it as though
-        // it never existed and throw a MissingInputException.
-        throw new MissingInputException(info, id);
-      });
+      return node.asset;
     });
   }
 
   /// Applies the transform so that it produces concrete (as opposed to lazy)
   /// outputs.
   Future _applyImmediate() {
     var newOutputs = new AssetSet();
     var transform = new Transform(this, newOutputs, _log);
 
     return syncFuture(() => transformer.apply(transform)).then((_) {
@@ skipping 71 matching lines @@
   void _log(AssetId asset, LogLevel level, String message, Span span) {
     // If the log isn't already associated with an asset, use the primary.
     if (asset == null) asset = primary.id;
     var entry = new LogEntry(info, asset, level, message, span);
     _onLogController.add(entry);
   }
 
   String toString() =>
     "transform node in $_location for $transformer on $primary";
 }