Fix bugs and add instrumentation

pkg/analyzer_plugin/lib/protocol/protocol.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 'dart:collection';
-
 import 'package:analyzer_plugin/protocol/protocol_generated.dart';
 import 'package:analyzer_plugin/src/protocol/protocol_internal.dart';
 
 /**
  * An interface for enumerated types in the protocol.
  *
  * Clients may not extend, implement or mix-in this class.
  */
 abstract class Enum {
   /**
@@ skipping 546 matching lines @@
     } catch (exception) {
       return null;
     }
   }
 
   /**
    * Return a table representing the structure of the Json object that will be
    * sent to the client to represent this response.
    */
   Map<String, Object> toJson() {
-    Map<String, Object> jsonObject = new HashMap<String, Object>();
+    Map<String, Object> jsonObject = <String, Object>{};
     jsonObject[ID] = id;
     if (error != null) {
       jsonObject[ERROR] = error.toJson();
     }
     if (result != null) {
       jsonObject[RESULT] = result;
     }
     return jsonObject;
   }
 }