Record first paint in UKM.

chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer.cc

Index: chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer.cc
diff --git a/chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer.cc b/chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer.cc
index 190c127b148ff1b7b050f417eceb63aa2315ded4..25b6b5ab513c05498a015e0c8bf9efd92edf89c5 100644
--- a/chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer.cc
+++ b/chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer.cc
@@ -19,6 +19,7 @@ const char kUkmParseStartName[] = "ParseTiming.NavigationToParseStart";
 const char kUkmDomContentLoadedName[] =
     "DocumentTiming.NavigationToDOMContentLoadedEventFired";
 const char kUkmLoadEventName[] = "DocumentTiming.NavigationToLoadEventFired";
+const char kUkmFirstPaintName[] = "PaintTiming.NavigationToFirstPaint";
 const char kUkmFirstContentfulPaintName[] =
     "PaintTiming.NavigationToFirstContentfulPaint";
 const char kUkmFirstMeaningfulPaintName[] =
@@ -165,6 +166,11 @@ void UkmPageLoadMetricsObserver::RecordTimingMetrics(
         internal::kUkmLoadEventName,
         timing.document_timing->load_event_start.value().InMilliseconds());
   }
+  if (timing.paint_timing->first_paint) {
+    builder->AddMetric(
+        internal::kUkmFirstPaintName,
+        timing.paint_timing->first_paint.value().InMilliseconds());
+  }
   if (timing.paint_timing->first_contentful_paint) {
     builder->AddMetric(
         internal::kUkmFirstContentfulPaintName,