[DevTools] Migrate from AgentStateCallbacks to DevToolsAgentHostObserver.

content/browser/devtools/devtools_agent_host_impl.h

Index: content/browser/devtools/devtools_agent_host_impl.h
diff --git a/content/browser/devtools/devtools_agent_host_impl.h b/content/browser/devtools/devtools_agent_host_impl.h
index 435f34e5e74e4e4763f9756b4289ced5b844e1ef..e5d309482d2ac59ac3829931a0a714a1d61dd375 100644
--- a/content/browser/devtools/devtools_agent_host_impl.h
+++ b/content/browser/devtools/devtools_agent_host_impl.h
@@ -73,17 +73,18 @@ class CONTENT_EXPORT DevToolsAgentHostImpl : public DevToolsAgentHost,
 
   int session_id() { DCHECK(client_); return session_id_; }
 
-  static void NotifyCallbacks(DevToolsAgentHostImpl* agent_host, bool attached);
-
  private:
   friend class DevToolsAgentHost; // for static methods
   bool InnerAttach(DevToolsAgentHostClient* client, bool force);
   void InnerDetach();
+  void NotifyAttached();
+  void NotifyDetached();
 
   const std::string id_;
   int session_id_;
   DevToolsAgentHostClient* client_;
   devtools::DevToolsIOContext io_context_;
+  static int s_attached_count_;
 };
 
 class DevToolsMessageChunkProcessor {