headless: Implement DevTools events

headless/public/internal/message_dispatcher.h

 // Copyright 2016 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 HEADLESS_PUBLIC_INTERNAL_MESSAGE_DISPATCHER_H_
 #define HEADLESS_PUBLIC_INTERNAL_MESSAGE_DISPATCHER_H_
 
 namespace headless {
 namespace internal {
 
 // An internal interface for sending DevTools messages from the domain agents.
 class MessageDispatcher {
  public:
   virtual void SendMessage(
       const char* method,
       std::unique_ptr<base::Value> params,
       base::Callback<void(const base::Value&)> callback) = 0;
   virtual void SendMessage(const char* method,
                            std::unique_ptr<base::Value> params,
                            base::Callback<void()> callback) = 0;
   virtual void SendMessage(
       const char* method,
       base::Callback<void(const base::Value&)> callback) = 0;
   virtual void SendMessage(const char* method,
                            base::Callback<void()> callback) = 0;
+
+  virtual void RegisterEventHandler(
+      const char* method,
+      base::Callback<void(const base::Value&)> callback) = 0;
 };
 
 }  // namespace internal
 }  // namespace headless
 
 #endif  // HEADLESS_PUBLIC_INTERNAL_MESSAGE_DISPATCHER_H_