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

lib/src/info.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.
 
 /**
  * Datatypes holding information extracted by the analyzer and used by later
  * phases of the compiler.
  */
 library info;
 
@@ skipping 49 matching lines @@
   /**
    * Checks if [input] is valid. It must be in [_baseDir] and must not be in
    * the [_outputDir].
    *
    * Adds emitted error/warning messages to [messages], if [messages] is
    * supplied.
    */
   bool checkInputPath(String input, Messages messages) {
     if (_mangleFilenames) return true;
     var canonicalized = path.normalize(input);
-    if (!path.relative(canonicalized, from: _outputDir).startsWith('../')) {
+    var parentDir = '..${path.separator}';
+    if (!path.relative(canonicalized, from: _outputDir).startsWith(parentDir)) {
       messages.error(
           'The file ${input} cannot be processed. '
           'Files cannot be under the output folder (${_outputDir}).',
           null, file: input);
       return false;
     }
-    if (path.relative(canonicalized, from: _baseDir).startsWith('../')) {
+    if (path.relative(canonicalized, from: _baseDir).startsWith(parentDir)) {
       messages.error(
           'The file ${input} cannot be processed. '
           'All processed files must be under the base folder (${_baseDir}), you'
           ' can specify the base folder using the --basedir flag.',
           null, file: input);
       return false;
     }
     return true;
   }
 
@@ skipping 649 matching lines @@
   }
 
   visitChildren(ElementInfo info) {
     for (var child in info.children) {
       var result = visit(child);
       if (result != null) return result;
     }
     return null;
   }
 }