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

pkg/polymer/lib/transformer.dart

Index: pkg/polymer/lib/transformer.dart
diff --git a/pkg/polymer/lib/transformer.dart b/pkg/polymer/lib/transformer.dart
index ebbfc121ffe04e013192ee15c417ad1f6051dc87..eb831a953d9492f5af95047d990bea916f61e153 100644
--- a/pkg/polymer/lib/transformer.dart
+++ b/pkg/polymer/lib/transformer.dart
@@ -12,6 +12,7 @@ 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';
 
@@ -82,6 +83,7 @@ List<List<Transformer>> createDeployPhases(
     [new ObservableTransformer()],
     [new ScriptCompactor(options, sdkDir: sdkDir)],
     [new PolyfillInjector(options)],
-    [new BuildFilter(options)]
+    [new BuildFilter(options)],
+    [new BuildLogCombiner(options)],
   ]);
 }