Move PubPackageMapProvider to its own file.

pkg/analyzer/test/source/package_map_provider_test.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 test.package.map.provider;
 
 import 'dart:convert';
 
 import 'package:analyzer/source/package_map_provider.dart';
+import 'package:analyzer/source/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/src/generated/sdk_io.dart';
 import 'package:unittest/unittest.dart';
 
 main() {
   groupSep = ' | ';
 
   group('PubPackageMapProvider', () {
     group('parsePackageMap', () {
@@ skipping 79 matching lines @@
         resourceProvider.newFolder(projectPath);
         resourceProvider.newFile(dependencyPath, 'contents');
         Set<String> dependencies = parsePackageMap(
             {'packages': {}, 'input_files': [relativeDependencyPath]}).dependencies;
         expect(dependencies, hasLength(1));
         expect(dependencies, contains(dependencyPath));
       });
     });
   });
 }