[DevTools] Migrate from AgentStateCallbacks to DevToolsAgentHostObserver.

content/browser/devtools/devtools_manager.h

 // Copyright (c) 2012 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_MANAGER_H_
 #define CONTENT_BROWSER_DEVTOOLS_DEVTOOLS_MANAGER_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
@@ skipping 14 matching lines @@
  public:
   // Returns single instance of this class. The instance is destroyed on the
   // browser main loop exit so this method MUST NOT be called after that point.
   static DevToolsManager* GetInstance();
 
   DevToolsManager();
   virtual ~DevToolsManager();
 
   DevToolsManagerDelegate* delegate() const { return delegate_.get(); }
 
-  void AgentHostStateChanged(DevToolsAgentHostImpl* agent_host, bool attached);
-
   void SetHttpHandler(std::unique_ptr<DevToolsHttpHandler> http_handler);
 
  private:
   friend struct base::DefaultSingletonTraits<DevToolsManager>;
 
   std::unique_ptr<DevToolsManagerDelegate> delegate_;
   std::unique_ptr<DevToolsHttpHandler> http_handler_;
-  int attached_hosts_count_;
 
   DISALLOW_COPY_AND_ASSIGN(DevToolsManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVTOOLS_DEVTOOLS_MANAGER_H_