Add support for lazy transformers.

pkg/barback/lib/src/package_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.package_graph;
 
 import 'dart:async';
 
 import 'asset_cascade.dart';
 import 'asset_id.dart';
 import 'asset_node.dart';
 import 'asset_set.dart';
 import 'build_result.dart';
 import 'errors.dart';
 import 'log.dart';
 import 'package_provider.dart';
-import 'pool.dart';
 import 'transformer.dart';
 import 'utils.dart';
 
 /// The collection of [AssetCascade]s for an entire application.
 ///
 /// This tracks each package's [AssetCascade] and routes asset requests between
 /// them.
 class PackageGraph {
   /// The provider that exposes asset and package information.
   final PackageProvider provider;
@@ skipping 104 matching lines @@
     var cascade = _cascades[id.package];
     if (cascade != null) return cascade.getAssetNode(id);
     return new Future.value(null);
   }
 
   /// Gets all output assets.
   ///
   /// If a build is currently in progress, waits until it completes. The
   /// returned future will complete with an error if the build is not
   /// successful.
+  ///
+  /// Any transforms using [LazyTransformer]s will be forced to generate
+  /// concrete outputs, and those outputs will be returned.
   Future<AssetSet> getAllAssets() {
+    for (var cascade in _cascades.values) {
+      cascade.forceAllTransforms();
+    }
+
     if (_cascadeResults.values.contains(null)) {
       // A build is still ongoing, so wait for it to complete and try again.
       return results.first.then((_) => getAllAssets());
     }
 
     // If an unexpected error occurred, complete with that.
     if (_lastUnexpectedError != null) {
       var error = _lastUnexpectedError;
       _lastUnexpectedError = null;
       return new Future.error(error, _lastUnexpectedErrorTrace);
@@ skipping 32 matching lines @@
       if (cascade == null) throw new ArgumentError("Unknown package $package.");
       cascade.removeSources(ids);
     });
   }
 
   void updateTransformers(String package,
       Iterable<Iterable<Transformer>> transformers) {
     _cascades[package].updateTransformers(transformers);
   }
 }