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

lib/dwc.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.
 
 /** The entry point to the compiler. Used to implement `bin/dwc.dart`. */
 library dwc;
 
 import 'dart:io';
 import 'package:logging/logging.dart' show Level;
 import 'src/compiler.dart';
@@ skipping 44 matching lines @@
  * Runs the web components compiler with the command-line options in [args].
  * See [CompilerOptions] for the definition of valid arguments.
  */
 // TODO(jmesserly): fix this to return a proper exit code
 // TODO(justinfagnani): return messages in the result
 Future<CompilerResult> run(List<String> args) {
   var options = CompilerOptions.parse(args);
   if (options == null) return new Future.immediate(new CompilerResult());
 
   fileSystem = new ConsoleFileSystem();
-  messages = new Messages(options: options);
+  messages = new Messages(options: options, shouldPrint: true);
 
   return asyncTime('Total time spent on ${options.inputFile}', () {
     var currentDir = new Directory.current().path;
     var compiler = new Compiler(fileSystem, options, currentDir);
     var res;
     return compiler.run()
       .transform((_) => (res = new CompilerResult._(messages, compiler.output)))
       .chain((_) => symlinkPubPackages(res, options))
       .chain((_) => emitFiles(compiler.output, options.clean))
       .transform((_) => res);
@@ skipping 99 matching lines @@
         null);
     }
     return null;
   });
 }
 
 
 // TODO(sigmund): this conversion from dart:io paths to internal paths should
 // go away when dartbug.com/5818 is fixed.
 Path _convert(fs.Path path) => new Path(path.toString());