Fix barback test failures.

pkg/barback/test/package_graph/declaring_transformer_test.dart

 // Copyright (c) 2014, 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.test.package_graph.declaring_transformer_test;
 
 import 'package:barback/barback.dart';
 import 'package:barback/src/utils.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
@@ skipping 79 matching lines @@
 
   test("a declaring transformer following a lazy transformer runs eagerly once "
       "its input is available", () {
     var declaring = new DeclaringRewriteTransformer("two", "three");
     initGraph(["app|foo.in"], {"app": [
       [new LazyAssetsTransformer(["app|out.one", "app|out.two"])],
       [declaring]
     ]});
 
     updateSources(["app|foo.in"]);
+    // Give the transformers time to declare their assets.
+    schedule(pumpEventQueue);
+
     expectAsset("app|out.one", "app|out.one");
     buildShouldSucceed();
 
     expect(declaring.numRuns, completion(equals(1)));
   });
 
   test("a declaring transformer following a lazy transformer doesn't re-run if "
       "its input becomes available and then unavailable", () {
     var declaring = new DeclaringRewriteTransformer("two", "three");
     initGraph(["app|foo.in"], {"app": [
       [new LazyAssetsTransformer(["app|out.one", "app|out.two"])],
       [declaring]
     ]});
 
     // Start [declaring] running, because its input became available.
     declaring.pauseApply();
     updateSources(["app|foo.in"]);
+    // Give the transformers time to declare their assets.
+    schedule(pumpEventQueue);
+
     expectAsset("app|out.one", "app|out.one");
     expectAssetDoesNotComplete("app|out.three");
 
     // Now [declaring]'s input is dirty, so it shouldn't re-run without an
     // explicit request.
     updateSources(["app|foo.in"]);
     declaring.resumeApply();
     buildShouldSucceed();
 
     // [declaring] should only have run once, despite its input changing. After
@@ skipping 84 matching lines @@
   test("can declare outputs it doesn't emit", () {
     initGraph(["app|foo.txt"], {"app": [
       [new DeclareAssetsTransformer(["app|out.txt"], [])]
     ]});
 
     updateSources(["app|foo.txt"]);
     expectNoAsset("app|out.txt");
     buildShouldSucceed();
   });
 }