Content Settings: Add RevocationObserver to measure when permissions are revoked

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_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,
       std::string resource_identifier) = 0;
 
+  // Fired when the content setting for an origin pair is changed from ALLOW to
+  // BLOCK or ASK. Only called when the user's preference is explicitly changed
+  // via HostContentSettingsMap::SetContentSettingDefaultScope().
+  virtual void OnContentSettingRevoked(
+      const GURL& primary_url,
+      const GURL& secondary_url,
+      ContentSettingsType content_type,
+      std::string resource_identifier) {};
+
  protected:
   virtual ~Observer() {}
 };
 
 }  // namespace content_settings
 
 #endif  // COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_OBSERVER_H_