Add UpdateViewportIntersection UKM metric

Bug: 1149691
Change-Id: I9d89fed2bab361c8ea34d24ed0a42f40041b09d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593246
Commit-Queue: Stefan Zager <szager@chromium.org>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840315}

third_party/blink/renderer/core/frame/local_frame_ukm_aggregator.cc

@@ -374,6 +374,7 @@ void LocalFrameUkmAggregator::ReportPreFCPEvent() {
       CASE_FOR_ID(JavascriptIntersectionObserver);
       CASE_FOR_ID(LazyLoadIntersectionObserver);
       CASE_FOR_ID(MediaIntersectionObserver);
+      CASE_FOR_ID(UpdateViewportIntersection);
       case kCount:
       case kMainFrame:
         NOTREACHED();
@@ -424,6 +425,7 @@ void LocalFrameUkmAggregator::ReportUpdateTimeEvent() {
       CASE_FOR_ID(JavascriptIntersectionObserver, i);
       CASE_FOR_ID(LazyLoadIntersectionObserver, i);
       CASE_FOR_ID(MediaIntersectionObserver, i);
+      CASE_FOR_ID(UpdateViewportIntersection, i);
       case kCount:
       case kMainFrame:
         NOTREACHED();

third_party/blink/renderer/core/frame/local_frame_ukm_aggregator.h

@@ -139,6 +139,7 @@ class CORE_EXPORT LocalFrameUkmAggregator
     kJavascriptIntersectionObserver,
     kLazyLoadIntersectionObserver,
     kMediaIntersectionObserver,
+    kUpdateViewportIntersection,
     kCount,
     kMainFrame
   };
@@ -175,7 +176,8 @@ class CORE_EXPORT LocalFrameUkmAggregator
         {"DisplayLockIntersectionObserver", true},
         {"JavascriptIntersectionObserver", true},
         {"LazyLoadIntersectionObserver", true},
-        {"MediaIntersectionObserver", true}};
+        {"MediaIntersectionObserver", true},
+        {"UpdateViewportIntersection", true}};
     static_assert(base::size(data) == kCount, "Metrics data mismatch");
     return data;
   }

third_party/blink/renderer/core/frame/local_frame_view.cc

@@ -4353,7 +4353,12 @@ bool LocalFrameView::UpdateViewportIntersectionsForSubtree(
     intersection_observation_state_ = kNotNeeded;
   }
 
-  UpdateViewportIntersection(flags, needs_occlusion_tracking);
+  {
+    SCOPED_UMA_AND_UKM_TIMER(
+        EnsureUkmAggregator(),
+        LocalFrameUkmAggregator::kUpdateViewportIntersection);
+    UpdateViewportIntersection(flags, needs_occlusion_tracking);
+  }
 
   for (Frame* child = frame_->Tree().FirstChild(); child;
        child = child->Tree().NextSibling()) {

tools/metrics/ukm/ukm.xml

@@ -2121,6 +2121,12 @@ be describing additional metrics about the same event.
       First Contentful Paint, in microseconds.
     </summary>
   </metric>
+  <metric name="UpdateViewportIntersection">
+    <summary>
+      Time spent computing internal geometry information about iframes, in
+      microseconds.
+    </summary>
+  </metric>
   <metric name="WaitForCommit">
     <summary>
       The time spent waiting for the compositor thread to begin processing a
@@ -3281,6 +3287,26 @@ be describing additional metrics about the same event.
       An int in the range [0,100].
     </summary>
   </metric>
+  <metric name="UpdateViewportIntersection">
+    <summary>
+      Time spent computing internal geometry information about iframes, in
+      microseconds.
+    </summary>
+    <aggregation>
+      <history>
+        <index fields="profile.country"/>
+        <statistics>
+          <quantiles type="std-percentiles"/>
+        </statistics>
+      </history>
+    </aggregation>
+  </metric>
+  <metric name="UpdateViewportIntersectionBeginMainFrame">
+    <summary>
+      The total main frame time used to compute internal geometry information
+      about iframes, in microseconds.
+    </summary>
+  </metric>
   <metric name="WaitForCommit">
     <summary>
       The time spent waiting for the compositor thread to begin processing a