Add a "session only" policy to the content settings.

chrome/common/content_settings.h

 // Copyright (c) 2010 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 CHROME_COMMON_CONTENT_SETTINGS_H_
 #define CHROME_COMMON_CONTENT_SETTINGS_H_
 
 #include "chrome/common/content_settings_types.h"
 
 // Different settings that can be assigned for a particular content type.  We
 // give the user the ability to set these on a global and per-host basis.
 enum ContentSetting {
   CONTENT_SETTING_DEFAULT = 0,
   CONTENT_SETTING_ALLOW,
   CONTENT_SETTING_BLOCK,
   CONTENT_SETTING_ASK,
+  CONTENT_SETTING_SESSION_ONLY,
   CONTENT_SETTING_NUM_SETTINGS
 };
 
 // Range-checked conversion of an int to a ContentSetting, for use when reading
 // prefs off disk.
 ContentSetting IntToContentSetting(int content_setting);
 
 // Aggregates the permissions for the different content types.
 struct ContentSettings {
   ContentSettings() {
     for (int i = 0; i < CONTENT_SETTINGS_NUM_TYPES; ++i)
       settings[i] = CONTENT_SETTING_DEFAULT;
   }
 
   explicit ContentSettings(ContentSetting default_setting) {
     for (int i = 0; i < CONTENT_SETTINGS_NUM_TYPES; ++i)
       settings[i] = default_setting;
   }
 
   ContentSetting settings[CONTENT_SETTINGS_NUM_TYPES];
 };
 
 #endif  // CHROME_COMMON_CONTENT_SETTINGS_H_