delete debug only files from output in release mode

pkg/polymer/lib/src/build/delete_file.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.
+
+/// Transformer that deletes everything that it sees, but only in release mode.
+library web_components.src.delete_file;
+
+import 'dart:async';
+import 'package:barback/barback.dart';
+
+// Deletes all files supplied in release mode.
+class DeleteFile extends Transformer {
+  BarbackSettings settings;
+
+  DeleteFile.asPlugin(this.settings);
+
+  /// Only apply to files that you want to be deleted in release mode.
+  Future<bool> isPrimary(idOrAsset) {
+    return new Future.value(settings.mode == BarbackMode.RELEASE);

[Siggi Cherem (dart-lang), 2014/09/03 16:56:02]

same here: 
  bool isPrimary(_) => settings.mode == BarbackMode.RELEASE;

[jakemac, 2014/09/03 17:45:42]

Done.

+  }
+
+  Future apply(Transform transform) {
+    transform.consumePrimary();
+    return new Future(() {});

[Siggi Cherem (dart-lang), 2014/09/03 16:56:02]

I wonder if this is needed by barback, or can we just return nothing.

[jakemac, 2014/09/03 17:45:42]

Done.

+  }
+}