diff --git a/metrics_utils.h b/metrics_utils.h
index d08cc4a..8f1aad1 100644
--- a/metrics_utils.h
+++ b/metrics_utils.h
@@ -87,10 +87,16 @@
 // Persists the finished time of an update to the |kPrefsSystemUpdatedMarker|.
 void SetSystemUpdatedMarker(ClockInterface* clock, PrefsInterface* prefs);
 
-// Persists the start time of an update to |kPrefsUpdateTimestampStart|.
+// Persists the start monotonic time of an update to
+// |kPrefsUpdateTimestampStart|.
 void SetUpdateTimestampStart(const base::Time& update_start_time,
                              PrefsInterface* prefs);
 
+// Persists the start boot time of an update to
+// |kPrefsUpdateBootTimestampStart|.
+void SetUpdateBootTimestampStart(const base::Time& update_start_boot_time,
+                                 PrefsInterface* prefs);
+
 // Called at program startup if the device booted into a new update.
 // The |time_to_reboot| parameter contains the (monotonic-clock) duration
 // from when the update successfully completed (the value in