[DevTools] Make DevToolsSession own it's DevToolsMessageChunkProcessor

content/browser/devtools/devtools_agent_host_impl.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_AGENT_HOST_IMPL_H_
 #define CONTENT_BROWSER_DEVTOOLS_DEVTOOLS_AGENT_HOST_IMPL_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 73 matching lines @@
   static int s_attached_count_;
   static int s_force_creation_count_;
 };
 
 class DevToolsMessageChunkProcessor {
  public:
   using SendMessageCallback = base::Callback<void(int, const std::string&)>;
   explicit DevToolsMessageChunkProcessor(const SendMessageCallback& callback);
   ~DevToolsMessageChunkProcessor();
 
-  std::string state_cookie() const { return state_cookie_; }
+  const std::string& state_cookie() const { return state_cookie_; }
   void set_state_cookie(const std::string& cookie) { state_cookie_ = cookie; }
   int last_call_id() const { return last_call_id_; }
   bool ProcessChunkedMessageFromAgent(const DevToolsMessageChunk& chunk);
   void Reset();
 
  private:
   SendMessageCallback callback_;
   std::string message_buffer_;
   uint32_t message_buffer_size_;
   std::string state_cookie_;
   int last_call_id_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVTOOLS_DEVTOOLS_AGENT_HOST_IMPL_H_