Fix MockSdk.fromFileUri() implementations.

pkg/analysis_server/test/mock_sdk.dart

 // Copyright (c) 2014, 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 testing.mock_sdk;
 
 import 'package:analyzer/file_system/file_system.dart' as resource;
 import 'package:analyzer/file_system/memory_file_system.dart' as resource;
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 316 matching lines @@
   List<String> get uris {
     List<String> uris = <String>[];
     for (SdkLibrary library in LIBRARIES) {
       uris.add(library.shortName);
     }
     return uris;
   }
 
   @override
   Source fromFileUri(Uri uri) {
-    String filePath = uri.path;
-    String libPath = '/lib';
-    if (!filePath.startsWith("$libPath/")) {
-      return null;
-    }
-    for (SdkLibrary library in LIBRARIES) {
-      String libraryPath = library.path;
-      if (filePath.replaceAll('\\', '/') == libraryPath) {
+    String filePath = provider.pathContext.fromUri(uri);
+    for (SdkLibrary library in sdkLibraries) {
+      String libraryPath = provider.convertPath(library.path);
+      if (filePath == libraryPath) {
         try {
-          resource.File file = provider.getResource(uri.path);
+          resource.File file = provider.getResource(filePath);
           Uri dartUri = Uri.parse(library.shortName);
           return file.createSource(dartUri);
         } catch (exception) {
           return null;
         }
       }
-      if (filePath.startsWith("$libraryPath/")) {
-        String pathInLibrary = filePath.substring(libraryPath.length + 1);
-        String path = '${library.shortName}/$pathInLibrary';
+      String libraryRootPath = provider.pathContext.dirname(libraryPath) +
+          provider.pathContext.separator;
+      if (filePath.startsWith(libraryRootPath)) {
+        String pathInLibrary = filePath.substring(libraryRootPath.length);
+        String uriStr = '${library.shortName}/$pathInLibrary';
         try {
-          resource.File file = provider.getResource(uri.path);
-          Uri dartUri = new Uri(scheme: 'dart', path: path);
+          resource.File file = provider.getResource(filePath);
+          Uri dartUri = Uri.parse(uriStr);
           return file.createSource(dartUri);
         } catch (exception) {
           return null;
         }
       }
     }
     return null;
   }
 
   @override
@@ skipping 80 matching lines @@
   bool get isInternal => shortName.startsWith('dart:_');
 
   @override
   bool get isShared => throw unimplemented;
 
   @override
   bool get isVmLibrary => throw unimplemented;
 
   UnimplementedError get unimplemented => new UnimplementedError();
 }