Fix more tests under windows

pkg/analyzer/test/src/task/strong/strong_test_helper.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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 library analyzer.test.src.task.strong.strong_test_helper;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 28 matching lines @@
 /// create a file like:
 ///
 ///     addFile('''
 ///       String x = /*error:STATIC_TYPE_ERROR*/3;
 ///     ''');
 ///     check();
 ///
 /// For a single file, you may also use [checkFile].
 void addFile(String content, {String name: '/main.dart'}) {
   name = name.replaceFirst('^package:', '/packages/');
-  files.newFile(name, content);
+  files.newFile(files.convertPath(name), content);
 }
 
 /// Run the checker on a program, staring from '/main.dart', and verifies that
 /// errors/warnings/hints match the expected value.
 ///
 /// See [addFile] for more information about how to encode expectations in
 /// the file text.
 ///
 /// Returns the main resolved library. This can be used for further checks.
 CompilationUnit check(
     {bool implicitCasts: true,
     bool implicitDynamic: true,
     List<String> nonnullableTypes: AnalysisOptionsImpl.NONNULLABLE_TYPES}) {
   _checkCalled = true;
 
-  expect(files.getFile('/main.dart').exists, true,
+  expect(files.getFile(files.convertPath('/main.dart')).exists, true,
       reason: '`/main.dart` is missing');
 
   var uriResolver = new _TestUriResolver(files);
   // Enable task model strong mode
   var context = AnalysisEngine.instance.createAnalysisContext();
   AnalysisOptionsImpl options = context.analysisOptions as AnalysisOptionsImpl;
   options.strongMode = true;
   options.strongModeHints = true;
   options.implicitCasts = implicitCasts;
   options.implicitDynamic = implicitDynamic;
@@ skipping 323 matching lines @@
 
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     if (uri.scheme == 'package') {
       return (provider.getResource('/packages/' + uri.path) as File)
           .createSource(uri);
     }
     return super.resolveAbsolute(uri, actualUri);
   }
 }