Add metric with time between background tab being foregrounded and the first paint

components/page_load_metrics/browser/page_load_metrics_observer.cc

Index: components/page_load_metrics/browser/page_load_metrics_observer.cc
diff --git a/components/page_load_metrics/browser/page_load_metrics_observer.cc b/components/page_load_metrics/browser/page_load_metrics_observer.cc
index b41c347c1f9a827aa3609efc5a728c753c9cd830..7ec32f8ca40ca153973a9949d7f3ebd621561226 100644
--- a/components/page_load_metrics/browser/page_load_metrics_observer.cc
+++ b/components/page_load_metrics/browser/page_load_metrics_observer.cc
@@ -7,8 +7,8 @@
 namespace page_load_metrics {
 
 PageLoadExtraInfo::PageLoadExtraInfo(
-    const base::TimeDelta& first_background_time,
-    const base::TimeDelta& first_foreground_time,
+    base::TimeDelta first_background_time,
+    base::TimeDelta first_foreground_time,
     bool started_in_foreground,
     const GURL& committed_url,
     const base::TimeDelta& time_to_commit,