Clean up warnings and hints

pkg/analyzer/test/resource_utils.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.test.resource_utils;
 
 import 'dart:async';
-import 'dart:core' hide Resource;
+import 'dart:core';
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/util/absolute_path.dart';
 import 'package:path/path.dart' as path;
 import 'package:unittest/unittest.dart';
 
 bool get isWindows => path.Style.platform == path.Style.windows;
 
@@ skipping 111 matching lines @@
         fail('Expected windows path, but found: $path');
       }
     } else {
       if (path.contains('\\')) {
         fail('Expected posix path, but found: $path');
       }
     }
     return path;
   }
 }