(Fix #215) better error printing in editor & extension, adds mapping for editor

bin/dwc_browser.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Compiles Dart Web Components from within a Chrome extension.
  * The Chrome extension logic exists outside of Dart as Dart does not support
  * Chrome extension APIs at this time.
  */
 library dwc_browser;
@@ skipping 32 matching lines @@
   // TODO(jacobr): provide a way to pass in options.
   var options = CompilerOptions.parse(['--no-colors', uri.path]);
   messages = new Messages(options: options);
   asyncTime('Compiled $sourceUri', () {
     var compiler = new Compiler(fileSystem, options);
     return compiler.run().chain((_) {
       for (var file in compiler.output) {
         fileSystem.writeString(file.path, file.contents);
       }
       var ret = fileSystem.flush();
+      js.scoped(() {
+        js.context.proxyMessages(sourcePagePort,

[Jennifer Messerly, 2012/12/06 04:00:08]

out of curiousity, can you inline proxyMessages?

sourcePagePort.postMessage(js.map({'type': 'MESSAGES', 'messages':
messages.messages.map((m) => '$m')}));

[Siggi Cherem (dart-lang), 2012/12/06 18:46:42]

yes, I believe so, I wasn't sure if 'map' worked ok, but I think it does. Here I
just wanted to follow the pattern Jacob started by adding some abstraction from
the background.js file. 

+            js.array(messages.messages.map((m) => m.toString())));
+      });
       js.release(sourcePagePort);
       return ret;
     });
   }, printTime: true);
 }