Add NavigationToFirstContentfulPaint UMA for ServiceWorker controlled pages.

chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc

Index: chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc
diff --git a/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc b/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc
index 148ee64622f2ba6eed00bd1b56a6fa76f5cb1ffd..dba24783ce2906bce5645c3db78bb4a8c1b0fb97 100644
--- a/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc
+++ b/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc
@@ -97,6 +97,9 @@ const char
         "PageLoad.Timing2.ParseBlockedOnScriptLoadFromDocumentWrite."
         "ParseComplete.Background";
 
+const char kServiceWorkerHistogramFirstContentfulPaint[] =
+    "PageLoad.Timing2.NavigationToFirstContentfulPaint.ServiceWorker";
+
 const char kHistogramFirstContentfulPaintHigh[] =
     "PageLoad.Timing2.NavigationToFirstContentfulPaint.HighResolutionClock";
 const char kHistogramFirstContentfulPaintLow[] =
@@ -282,6 +285,11 @@ void CorePageLoadMetricsObserver::RecordTimingHistograms(
         PAGE_LOAD_HISTOGRAM(internal::kHistogramFirstContentfulPaintLow,
                             timing.first_contentful_paint);
       }
+      if (!timing.worker_start.is_null()) {
+        PAGE_LOAD_HISTOGRAM(
+            internal::kServiceWorkerHistogramFirstContentfulPaint,
+            timing.first_contentful_paint);
+      }
       PAGE_LOAD_HISTOGRAM(internal::kHistogramDomLoadingToFirstContentfulPaint,
                           timing.first_contentful_paint - timing.dom_loading);
     } else {