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

prefs.cc

 // 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.
 
 #include "update_engine/prefs.h"
 
 #include <base/file_util.h>
 #include <base/logging.h>
 #include <base/string_number_conversions.h>
 #include <base/string_util.h>
 
 #include "update_engine/utils.h"
 
 using std::string;
 
 namespace chromeos_update_engine {
 
 const char kPrefsDeltaUpdateFailures[] = "delta-update-failures";
 const char kPrefsLastActivePingDay[] = "last-active-ping-day";
 const char kPrefsLastRollCallPingDay[] = "last-roll-call-ping-day";
 const char kPrefsManifestMetadataSize[] = "manifest-metadata-size";
+const char kPrefsPreviousVersion[] = "previous-version";
 const char kPrefsResumedUpdateFailures[] = "resumed-update-failures";
 const char kPrefsUpdateCheckResponseHash[] = "update-check-response-hash";
 const char kPrefsUpdateStateNextDataOffset[] = "update-state-next-data-offset";
 const char kPrefsUpdateStateNextOperation[] = "update-state-next-operation";
 const char kPrefsUpdateStateSHA256Context[] = "update-state-sha-256-context";
 const char kPrefsUpdateStateSignedSHA256Context[] =
     "update-state-signed-sha-256-context";
 
 bool Prefs::Init(const FilePath& prefs_dir) {
   prefs_dir_ = prefs_dir;
@@ skipping 39 matching lines @@
   for (size_t i = 0; i < key.size(); ++i) {
     char c = key.at(i);
     TEST_AND_RETURN_FALSE(IsAsciiAlpha(c) || IsAsciiDigit(c) ||
                           c == '_' || c == '-');
   }
   *filename = prefs_dir_.Append(key);
   return true;
 }
 
 }  // namespace chromeos_update_engine