(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 24 matching lines @@
  * See extension/background.js.
  */
 void parse(js.Proxy sourcePagePort, String sourceUri) {
   // TODO(jacobr): we need to send error messages back to sourcePagePort.
   js.retain(sourcePagePort);
   print("Processing: $sourceUri");
   Uri uri = new Uri.fromString(sourceUri);
   fileSystem = new BrowserFileSystem(uri.scheme, sourcePagePort);
   // TODO(jacobr): provide a way to pass in options.
   var options = CompilerOptions.parse(['--no-colors', uri.path]);
-  messages = new Messages(options: options);
+  messages = new Messages(options: options, shouldPrint: false);
   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,
+            js.array(messages.messages.map(
+                (m) => [m.level.name, m.toString()])));
+      });
       js.release(sourcePagePort);
       return ret;
     });
   }, printTime: true);
 }