Fix path bug in windows, don't emit code altogether if we have already seen

lib/src/dart_parser.dart

 // Copyright (c) 2013, 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.
 
 /**
  * Parser for Dart code based on the experimental analyzer.
  */
 library dart_parser;
 
 import 'dart:utf';
@@ skipping 122 matching lines @@
   var token = scanner.tokenize();
   var parser = new Parser(null, errorListener);
   var unit = parser.parseCompilationUnit(token);
 
   if (path == null || messages == null) return unit;
 
   // TODO(jmesserly): removed this for now because the analyzer doesn't format
   // messages properly, so you end up with things like "Unexpected token '%s'".
   // This used to convert parser messages into our messages. Enable this
   // once analyzer is fixed.
+  // TODO(sigmund): once we enable this, we need to fix compiler.dart to clear
+  // out the output of the compiler if we see compilation errors.
   if (false) {
     var file = new File.text(path, code);
     for (var e in errorListener.errors) {
       var span = file.span(e.offset, e.offset + e.length);
 
       var severity = e.errorCode.errorSeverity;
       if (severity == ErrorSeverity.ERROR) {
         messages.error(e.message, span, file: path);
       } else {
         assert(severity == ErrorSeverity.WARNING);
         messages.warning(e.message, span, file: path);
       }
     }
   }
 
   return unit;
 }
 
 class _ErrorCollector extends AnalysisErrorListener {
   final errors = new List<AnalysisError>();
   onError(error) => errors.add(error);
 }