Polymer transformer logs now show on the frontend for pub serve.

pkg/polymer/lib/transformer.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.
 
 /// Transfomer used for pub-serve and pub-deploy.
 library polymer.transformer;
 
 import 'package:barback/barback.dart';
 import 'package:observe/transformer.dart';
 
 import 'src/build/build_filter.dart';
 import 'src/build/common.dart';
 import 'src/build/import_inliner.dart';
 import 'src/build/linter.dart';
+import 'src/build/build_log_combiner.dart';
 import 'src/build/polyfill_injector.dart';
 import 'src/build/script_compactor.dart';
 
 /// The Polymer transformer, which internally runs several phases that will:
 ///   * Extract inlined script tags into their separate files
 ///   * Apply the observable transformer on every Dart script.
 ///   * Inline imported html files
 ///   * Combine scripts from multiple files into a single script tag
 ///   * Inject extra polyfills needed to run on all browsers.
 ///
@@ skipping 50 matching lines @@
     TransformOptions options, {String sdkDir}) {
   // TODO(sigmund): this should be done differently. We should lint everything
   // that is reachable and have the option to lint the rest (similar to how
   // dart2js can analyze reachable code or entire libraries).
   var phases = options.lint ? [[new Linter(options)]] : [];
   return phases..addAll([
     [new ImportInliner(options)],
     [new ObservableTransformer()],
     [new ScriptCompactor(options, sdkDir: sdkDir)],
     [new PolyfillInjector(options)],
-    [new BuildFilter(options)]
+    [new BuildFilter(options)],
+    [new BuildLogCombiner(options)],
   ]);
 }