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

bin/dwc_browser.dart

Index: bin/dwc_browser.dart
diff --git a/bin/dwc_browser.dart b/bin/dwc_browser.dart
index 157a0591fa0f8dbf15c8c6a054712c4caba0c720..720aea9eb569205ab40a8a0dc37dfd8fe3e7d5d6 100644
--- a/bin/dwc_browser.dart
+++ b/bin/dwc_browser.dart
@@ -50,6 +50,10 @@ void parse(js.Proxy sourcePagePort, String sourceUri) {
         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;
     });