[DevTools] Migrate DevToolsTracingHandler to generated handler.

content/browser/devtools/devtools_protocol.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_DEVTOOLS_DEVTOOLS_PROTOCOL_H_
 #define CONTENT_BROWSER_DEVTOOLS_DEVTOOLS_PROTOCOL_H_
 
 #include <map>
 #include <string>
 
@@ skipping 96 matching lines @@
     DISALLOW_COPY_AND_ASSIGN(Response);
   };
 
   class Notification : public Message {
    public:
 
     virtual std::string Serialize() override;
 
    private:
     friend class DevToolsProtocol;
+    friend class DevToolsProtocolClient;
     virtual ~Notification();
 
     // Takes ownership of |params|.
     Notification(const std::string& method,
                  base::DictionaryValue* params);
 
     DISALLOW_COPY_AND_ASSIGN(Notification);
   };
 
   class CONTENT_EXPORT Handler {
@@ skipping 59 matching lines @@
   static scoped_refptr<Notification> CreateNotification(
       const std::string& method, base::DictionaryValue* params);
 
   DevToolsProtocol() {}
   ~DevToolsProtocol() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVTOOLS_DEVTOOLS_PROTOCOL_H_