AU: Send a previous version event after reboot following an update.

prefs_interface.h

 // Copyright (c) 2010 The Chromium OS 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 CHROMEOS_PLATFORM_UPDATE_ENGINE_PREFS_INTERFACE_H__
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_PREFS_INTERFACE_H__
 
 #include <string>
 
 namespace chromeos_update_engine {
 
 extern const char kPrefsDeltaUpdateFailures[];
 extern const char kPrefsLastActivePingDay[];
 extern const char kPrefsLastRollCallPingDay[];
 extern const char kPrefsManifestMetadataSize[];
+extern const char kPrefsPreviousVersion[];
 extern const char kPrefsResumedUpdateFailures[];
 extern const char kPrefsUpdateCheckResponseHash[];
 extern const char kPrefsUpdateStateNextDataOffset[];
 extern const char kPrefsUpdateStateNextOperation[];
 extern const char kPrefsUpdateStateSHA256Context[];
 extern const char kPrefsUpdateStateSignedSHA256Context[];
 
 // The prefs interface allows access to a persistent preferences
 // store. The two reasons for providing this as an interface are
 // testing as well as easier switching to a new implementation in the
@@ skipping 18 matching lines @@
   // Associates |key| with an int64 |value|. Returns true on success,
   // false otherwise.
   virtual bool SetInt64(const std::string& key, const int64_t value) = 0;
 
   virtual ~PrefsInterface() {}
 };
 
 }  // namespace chromeos_update_engine
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_PREFS_INTERFACE_H__