Add ParseStartToFirstContentfulPaint metric to @import css scanner

chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h b/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h
index 3cf6b07d5d437e11b03c5ca46d05bfe4d17c2f61..7af74a0206f081c537809f6fb5df01b87585dc75 100644
--- a/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h
+++ b/chrome/browser/page_load_metrics/observers/css_scanning_page_load_metrics_observer.h
@@ -15,6 +15,9 @@ class CssScanningMetricsObserver
   ~CssScanningMetricsObserver() override;
 
   // page_load_metrics::PageLoadMetricsObserver:
+  void OnFirstContentfulPaint(
+      const page_load_metrics::PageLoadTiming& timing,
+      const page_load_metrics::PageLoadExtraInfo& info) override;
   void OnFirstMeaningfulPaint(
       const page_load_metrics::PageLoadTiming& timing,
       const page_load_metrics::PageLoadExtraInfo& info) override;