Add support for built-in plugins

pkg/analyzer_plugin/lib/plugin/plugin.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 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart'
     show AnalysisDriverGeneric, AnalysisDriverScheduler, PerformanceLog;
 import 'package:analyzer/src/dart/analysis/file_state.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer_plugin/channel/channel.dart';
 import 'package:analyzer_plugin/protocol/protocol.dart';
 import 'package:analyzer_plugin/protocol/protocol_constants.dart';
 import 'package:analyzer_plugin/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/src/protocol/protocol_internal.dart';
 import 'package:analyzer_plugin/src/utilities/null_string_sink.dart';
@@ skipping 60 matching lines @@
   /**
    * The file content overlay used by any analysis drivers that are created.
    */
   final FileContentOverlay fileContentOverlay = new FileContentOverlay();
 
   /**
    * Initialize a newly created analysis server plugin. If a resource [provider]
    * is given, then it will be used to access the file system. Otherwise a
    * resource provider that accesses the physical file system will be used.
    */
-  ServerPlugin(this.resourceProvider) {
+  ServerPlugin(ResourceProvider provider)
+      : resourceProvider = provider ?? PhysicalResourceProvider.INSTANCE {
     analysisDriverScheduler = new AnalysisDriverScheduler(performanceLog);
     analysisDriverScheduler.start();
   }
 
   /**
    * Return the byte store used by any analysis drivers that are created, or
    * `null` if the cache location isn't known because the 'plugin.version'
    * request has not yet been received.
    */
   ByteStore get byteStore => _byteStore;
@@ skipping 428 matching lines @@
       response = new Response(id,
           error: new RequestError(
               RequestErrorCode.PLUGIN_ERROR, exception.toString(),
               stackTrace: stackTrace.toString()));
     }
     if (response != null) {
       _channel.sendResponse(response);
     }
   }
 }