Add UpdateEngine.SuccessfulUpdate.TotalDurationUptimeMinutes.

This is a new metric added in http://aosp/681827.

Bug: b:77884453
Change-Id: I0035cd3e50c440564640aae90e68d2ad7a891017
Reviewed-on: https://chromium-review.googlesource.com/1086280Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Sen Jiang <senj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564972}

tools/metrics/histograms/histograms.xml

@@ -102567,6 +102567,20 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="UpdateEngine.SuccessfulUpdate.TotalDurationUptimeMinutes"
+    units="minutes">
+  <owner>senj@chromium.org</owner>
+  <summary>
+    The total number of minutes from when an update was detected until an update
+    (possibly another update) was applied. This does not include the time
+    waiting for update checks and time the device spent sleeping.
+
+    This is reported on every successful update.
+
+    This metric is specific to Chrome OS.
+  </summary>
+</histogram>
+
 <histogram name="UpdateEngine.SuccessfulUpdate.UpdatesAbandonedCount"
     units="count">
   <owner>zeuthen@chromium.org</owner>