Log an immediate variant of FirstContentfulPaint.

chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h b/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h
index 13a52dc8ffcd22c357b926fe88dcfeef1fa3fc4d..93efe4044dc2d58d40d76605f24d52867893a1ea 100644
--- a/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h
+++ b/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h
@@ -20,6 +20,7 @@ extern const char kHistogramDomContentLoaded[];
 extern const char kHistogramDomLoadingToDomContentLoaded[];
 extern const char kHistogramLoad[];
 extern const char kHistogramFirstContentfulPaint[];
+extern const char kHistogramFirstContentfulPaintImmediate[];
 extern const char kHistogramDomLoadingToFirstContentfulPaint[];
 extern const char kHistogramParseDuration[];
 extern const char kHistogramParseBlockedOnScriptLoad[];
@@ -48,6 +49,9 @@ class CorePageLoadMetricsObserver
   ~CorePageLoadMetricsObserver() override;
 
   // page_load_metrics::PageLoadMetricsObserver:
+  void OnTimingUpdate(
+      const page_load_metrics::PageLoadTiming& timing,
+      const page_load_metrics::PageLoadExtraInfo& info) override;
   void OnComplete(const page_load_metrics::PageLoadTiming& timing,
                   const page_load_metrics::PageLoadExtraInfo& info) override;
   void OnFailedProvisionalLoad(
@@ -69,6 +73,7 @@ class CorePageLoadMetricsObserver
                     const page_load_metrics::PageLoadExtraInfo& info);
 
   FailedProvisionalLoadInfo failed_provisional_load_info_;
+  bool logged_first_contentful_paint_from_timing_update_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(CorePageLoadMetricsObserver);
 };