headless: Register event handlers on demand

headless/lib/browser/domain_h.template

 // This file is generated
 
 // Copyright (c) 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_DOMAINS_{{domain.domain | camelcase_to_hacker_style | upper}}_H_
 #define HEADLESS_PUBLIC_DOMAINS_{{domain.domain | camelcase_to_hacker_style | upper}}_H_
 
 #include "base/callback.h"
@@ skipping 102 matching lines @@
   {# Generate event dispatchers. #}
   {% for event in domain.events %}
   void Dispatch{{event.name | to_title_case}}Event(const base::Value& params);
   {% endfor %}
 
   internal::MessageDispatcher* dispatcher_;  // Not owned.
   {% if "events" in domain %}
   base::ObserverList<ExperimentalObserver> observers_;
   {% endif %}
 
+  {% if "events" in domain %}
+ protected:
+  void RegisterEventHandlersIfNeeded();
+
+  {% endif %}
  private:
+  {% if "events" in domain %}
+  bool event_handlers_registered_ = false;
+
+  {% endif %}
   DISALLOW_COPY_AND_ASSIGN(Domain);
 };
 
 class ExperimentalDomain : public Domain {
  public:
   ExperimentalDomain(internal::MessageDispatcher* dispatcher);
   ~ExperimentalDomain();
 
   {% if "events" in domain %}
   // Add or remove an observer. |observer| must be removed before being
@@ skipping 12 matching lines @@
   {% endfor %}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ExperimentalDomain);
 };
 
 }  // namespace {{domain.domain | camelcase_to_hacker_style}}
 }  // namespace headless
 
 #endif  // HEADLESS_PUBLIC_DOMAINS_{{domain.domain | camelcase_to_hacker_style | upper}}_H_