Attempt to fix DartEditBuilderImplTest on Windows.

pkg/analyzer_plugin/test/src/utilities/change_builder/change_builder_dart_test.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_resolution_map.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 1347 matching lines @@
     expect(edit.replacement, equalsIgnoringWhitespace('implements A, B'));
   }
 
   Future<Null> _assertImportLibraries(
       String initialCode, List<String> newUris, String expectedCode) async {
     String path = provider.convertPath('/test.dart');
     addSource(path, initialCode);
     DartChangeBuilderImpl builder = new DartChangeBuilderImpl(driver);
     await builder.addFileEdit(path, 1, (DartFileEditBuilder builder) {
       Iterable<_MockSource> sources = newUris.map((newUri) {
-        String path = newUri.contains(':') ? null : '/$newUri';
+        String path =
+            newUri.contains(':') ? null : provider.convertPath('/$newUri');
         return new _MockSource(path, Uri.parse(newUri));
       });
       builder.importLibraries(sources);
     });
 
     String resultCode = initialCode;
     List<SourceEdit> edits = getEdits(builder);
     for (SourceEdit edit in edits) {
       resultCode = edit.apply(resultCode);
     }
@@ skipping 106 matching lines @@
   @override
   final String fullName;
 
   @override
   final Uri uri;
 
   _MockSource(this.fullName, this.uri);
 
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }