Add UpdateViewportIntersection breakdowns for UMA

The UMA category was added by:

https://chromium-review.googlesource.com/c/chromium/src/+/2593246

Bug: 1149692
Change-Id: I6016fb72cc62ead7d8f91210a690793cccd693a6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2613346
Commit-Queue: Stefan Zager <szager@chromium.org>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841652}

tools/metrics/histograms/histograms_xml/blink/histograms.xml

@@ -2059,6 +2059,25 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Blink.UpdateViewportIntersection.UpdateTime"
+    units="microseconds" expires_after="2021-03-21">
+<!-- Name completed by histogram_suffixes name="BlinkUpdateTimePreFCPSuffixes" -->
+
+<!-- Name completed by histogram_suffixes name="BlinkUpdateTimePostFCPSuffixes" -->
+
+<!-- Name completed by histogram_suffixes name="BlinkUpdateTimeAggregatedSuffixes" -->
+
+  <owner>schenney@chromium.org</owner>
+  <owner>paint-dev@chromium.org</owner>
+  <summary>
+    Time spent computing geometry information about iframes from the perspective
+    of their embedding document. This time is also included in the
+    Blink.IntersectionObservation.UpdateTime metric.
+
+    This histogram only records metrics on machines with high-resolution clocks.
+  </summary>
+</histogram>
+
 <histogram name="Blink.UseCounter.AnimatedCSSProperties"
     enum="MappedCSSProperties" expires_after="never">
 <!-- expires-never: used by Chrome Platform Status dashboard -->

tools/metrics/histograms/histograms_xml/histogram_suffixes_list.xml

@@ -2007,6 +2007,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <affected-histogram name="Blink.ScrollingCoordinator.UpdateTime"/>
   <affected-histogram name="Blink.Style.UpdateTime"/>
   <affected-histogram name="Blink.StyleAndLayout.UpdateTime"/>
+  <affected-histogram name="Blink.UpdateViewportIntersection.UpdateTime"/>
   <affected-histogram name="Blink.WaitForCommit.UpdateTime"/>
 </histogram_suffixes>
 
@@ -2034,6 +2035,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <affected-histogram name="Blink.ScrollingCoordinator.UpdateTime"/>
   <affected-histogram name="Blink.Style.UpdateTime"/>
   <affected-histogram name="Blink.StyleAndLayout.UpdateTime"/>
+  <affected-histogram name="Blink.UpdateViewportIntersection.UpdateTime"/>
   <affected-histogram name="Blink.WaitForCommit.UpdateTime"/>
 </histogram_suffixes>
 
@@ -2061,6 +2063,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <affected-histogram name="Blink.ScrollingCoordinator.UpdateTime"/>
   <affected-histogram name="Blink.Style.UpdateTime"/>
   <affected-histogram name="Blink.StyleAndLayout.UpdateTime"/>
+  <affected-histogram name="Blink.UpdateViewportIntersection.UpdateTime"/>
   <affected-histogram name="Blink.WaitForCommit.UpdateTime"/>
 </histogram_suffixes>