[Do not commit] Track revocations in content_settings::Observer

components/content_settings/core/browser/content_settings_observer.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 COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_OBSERVER_H_
 #define COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_OBSERVER_H_
 
 #include <string>
 
+#include "components/content_settings/core/common/content_settings.h"
 #include "components/content_settings/core/common/content_settings_pattern.h"
 #include "components/content_settings/core/common/content_settings_types.h"
 
 namespace content_settings {
 
 class Observer {
  public:
   virtual void OnContentSettingChanged(
       const ContentSettingsPattern& primary_pattern,
       const ContentSettingsPattern& secondary_pattern,
       ContentSettingsType content_type,
+      ContentSetting previous_value,
       std::string resource_identifier) = 0;
 
  protected:
   virtual ~Observer() {}
 };
 
 }  // namespace content_settings
 
 #endif  // COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_OBSERVER_H_