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

update_attempter.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/update_attempter.h"
 
 // From 'man clock_gettime': feature test macro: _POSIX_C_SOURCE >= 199309L
 #ifndef _POSIX_C_SOURCE
 #define _POSIX_C_SOURCE 199309L
 #endif  // _POSIX_C_SOURCE
@@ skipping 271 matching lines @@
 
   if (status_ == UPDATE_STATUS_REPORTING_ERROR_EVENT) {
     LOG(INFO) << "Error event sent.";
     SetStatusAndNotify(UPDATE_STATUS_IDLE);
     return;
   }
 
   if (code == kActionCodeSuccess) {
     utils::WriteFile(kUpdateCompletedMarker, "", 0);
     prefs_->SetInt64(kPrefsDeltaUpdateFailures, 0);
+    prefs_->SetString(kPrefsPreviousVersion, omaha_request_params_.app_version);
     DeltaPerformer::ResetUpdateProgress(prefs_, false);
     SetStatusAndNotify(UPDATE_STATUS_UPDATED_NEED_REBOOT);
 
     // Report the time it took to update the system.
     int64_t update_time = time(NULL) - last_checked_time_;
     metrics_lib_->SendToUMA("Installer.UpdateTime",
                             static_cast<int>(update_time),  // sample
                             1,  // min = 1 second
                             20 * 60,  // max = 20 minutes
                             50);  // buckets
@@ skipping 268 matching lines @@
     uint64_t resume_offset = manifest_metadata_size + next_data_offset;
     if (resume_offset < response_handler_action_->install_plan().size) {
       fetcher->AddRange(resume_offset, -1);
     }
   } else {
     fetcher->AddRange(0, -1);
   }
 }
 
 }  // namespace chromeos_update_engine