fix embedder url mapping on Windows

pkg/analyzer/lib/source/embedder.dart

 // Copyright (c) 2015, 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.
 
 library analyzer.source.embedder;
 
 import 'dart:collection' show HashMap;
 import 'dart:core' hide Resource;
 
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 189 matching lines @@
   @override
   List<String> get uris => _librariesMap.uris;
 
   @override
   Source fromFileUri(Uri uri) {
     JavaFile file = new JavaFile.fromUri(uri);
     String filePath = file.getAbsolutePath();
 
     String path;
     for (SdkLibrary library in _librariesMap.sdkLibraries) {
-      String libraryPath = library.path;
+      String libraryPath = library.path.replaceAll('/', JavaFile.separator);
       if (filePath == libraryPath) {
         path = '$_DART_COLON_PREFIX${library.shortName}';
         break;
       }
     }
     if (path == null) {
       for (SdkLibrary library in _librariesMap.sdkLibraries) {
-        String libraryPath = library.path;
-        int index = libraryPath.lastIndexOf('/');
+        String libraryPath = library.path.replaceAll('/', JavaFile.separator);
+        int index = libraryPath.lastIndexOf(JavaFile.separator);
         if (index == -1) {
           continue;
         }
         String prefix = libraryPath.substring(0, index + 1);
         if (!filePath.startsWith(prefix)) {
           continue;
         }
-        var relPath = filePath.substring(prefix.length);
+        var relPath = filePath
+            .substring(prefix.length).replaceAll(JavaFile.separator, '/');
         path = '$_DART_COLON_PREFIX${library.shortName}/$relPath';
         break;
       }
     }
 
     if (path != null) {
       try {
         return new FileBasedSource(file, parseUriWithException(path));
       } on URISyntaxException catch (exception, stackTrace) {
         AnalysisEngine.instance.logger.logInformation(
@@ skipping 22 matching lines @@
     }
     SdkLibrary library = getSdkLibrary(libraryName);
     if (library == null) {
       return null;
     }
     String srcPath;
     if (relativePath.isEmpty) {
       srcPath = library.path;
     } else {
       String libraryPath = library.path;
-      int index = libraryPath.lastIndexOf('/');
+      int index = libraryPath.lastIndexOf(JavaFile.separator);
       if (index == -1) {
-        return null;
+        index = libraryPath.lastIndexOf('/');
+        if (index == -1) {
+          return null;
+        }
       }
       String prefix = libraryPath.substring(0, index + 1);
       srcPath = '$prefix$relativePath';
     }
     String filePath = srcPath.replaceAll('/', JavaFile.separator);
     try {
       JavaFile file = new JavaFile(filePath);
       return new FileBasedSource(file, parseUriWithException(dartUri));
     } on URISyntaxException {
       return null;
     }
   }
 }