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

pkg/polymer/lib/src/build/build_log_combiner.dart

Index: pkg/polymer/lib/src/build/build_log_combiner.dart
diff --git a/pkg/polymer/lib/src/build/build_log_combiner.dart b/pkg/polymer/lib/src/build/build_log_combiner.dart
new file mode 100644
index 0000000000000000000000000000000000000000..cfd85ca59b18c2c205162621055bc3aa200487f0
--- /dev/null
+++ b/pkg/polymer/lib/src/build/build_log_combiner.dart
@@ -0,0 +1,34 @@
+// 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.
+
+/// Logic to combine all the ._buildLog.* logs into one ._buildLog file.
+library polymer.src.build.log_combiner;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+import 'package:html5lib/parser.dart' show parseFragment;
+
+import 'common.dart';
+import 'wrapped_logger.dart';
+
+/// Logic to combine all the ._buildLog.* logs into one ._buildLog file.
+class BuildLogCombiner extends Transformer with PolymerTransformer {
+  final TransformOptions options;
+
+  BuildLogCombiner(this.options);
+
+  /// Run only on entry point html files and only if
+  /// options.injectBuildLogsInOutput is true.
+  bool isPrimary(idOrAsset) {
+    if (!options.injectBuildLogsInOutput) return false;
+    var id = idOrAsset is AssetId ? idOrAsset : idOrAsset.id;
+    return options.isHtmlEntryPoint(id);
+  }
+
+  Future apply(Transform transform) {
+    // Combine all ._buildLogs* files into one ._buildLogs file.
+    return WrappedLogger.combineLogFiles(transform);
+  }
+}