Add test-only constructor for PageLoadExtraInfo.

chrome/browser/page_load_metrics/page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/page_load_metrics_observer.h b/chrome/browser/page_load_metrics/page_load_metrics_observer.h
index 0f9cc76a98b28861db918463c35afafe9c0ba5f0..aec560c20262e97e071ce88906c22908c515a550 100644
--- a/chrome/browser/page_load_metrics/page_load_metrics_observer.h
+++ b/chrome/browser/page_load_metrics/page_load_metrics_observer.h
@@ -119,6 +119,10 @@ struct PageLoadExtraInfo {
       const base::Optional<base::TimeDelta>& page_end_time,
       const PageLoadMetadata& metadata);
 
+  // Simplified version of the constructor, intended for use in tests.
+  static PageLoadExtraInfo CreateForTesting(const GURL& url,
+                                            bool started_in_foreground);
+
   PageLoadExtraInfo(const PageLoadExtraInfo& other);
 
   ~PageLoadExtraInfo();