delete debug only files from output in release mode

pkg/polymer/lib/src/build/remove_sourcemap_comment.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 removes any sourcemap comments from javascript files.
+library web_components.src.remove_sourcemap_comment;
+
+import 'dart:async';
+import 'package:barback/barback.dart';
+
+/// Transformer that removes any sourcemap comments from javascript files.
+/// Comments should be on their own line in the form: //# sourceMappingURL=*.map
+class RemoveSourcemapComment extends Transformer {
+  BarbackSettings settings;
+
+  RemoveSourcemapComment.asPlugin(this.settings);
+
+  /// Only apply to files that you want to be deleted in release mode.
+  Future<bool> isPrimary(_) {
+    return new Future.value(settings.mode == BarbackMode.RELEASE);

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

same here 

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

Done.

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

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

I think this works also if you don't consume it, instead just do the addOutput
only when you'll modify it.

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

Done.

+    var id = transform.primaryInput.id;
+    return transform.readInputAsString(id).then((file) {
+      if (!file.contains(_SOURCE_MAP_COMMENT)) {
+        // Don't create a new asset if there are no changes.
+        transform.addOutput(transform.primaryInput);
+        return;
+      }
+      transform.addOutput(new Asset.fromString(
+          id, file.replaceAll(_SOURCE_MAP_COMMENT, '')));
+    });
+  }
+}
+
+final RegExp _SOURCE_MAP_COMMENT = new RegExp(r'\n\s*\/\/# sourceMappingURL.*');