Work around naming conflict in analyzer's Resource class.

pkg/analysis_server/test/source/caching_put_package_map_provider_test.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 test.source.caching_pub_package_map_provider;
 
 import 'dart:convert';
+import 'dart:core' hide Resource;
 import 'dart:io' as io;
 
 import 'package:analysis_server/src/source/caching_pub_package_map_provider.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/source/package_map_provider.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/sdk_io.dart';
 import 'package:unittest/unittest.dart';
 
@@ skipping 367 matching lines @@
       provider.newFolder(path);
     }
     int fileCount = _filePaths.length;
     for (int fileIndex = 0; fileIndex < fileCount; ++fileIndex) {
       String path = _filePaths[fileIndex];
       TimestampedData content = _fileContents[fileIndex];
       provider.newFile(path, content.data, content.modificationTime);
     }
   }
 }