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

components/page_load_metrics/browser/page_load_metrics_util.h

Index: components/page_load_metrics/browser/page_load_metrics_util.h
diff --git a/components/page_load_metrics/browser/page_load_metrics_util.h b/components/page_load_metrics/browser/page_load_metrics_util.h
index 375debb3f2bc0f2d61c94c6b5f19b6b0dd72a1b5..380c077d26357ae6db44339bbbdacfe9b45692b6 100644
--- a/components/page_load_metrics/browser/page_load_metrics_util.h
+++ b/components/page_load_metrics/browser/page_load_metrics_util.h
@@ -18,13 +18,15 @@ namespace page_load_metrics {
 struct PageLoadExtraInfo;
 struct PageLoadTiming;
 
-// Returns false for events for which we have no timing information, and events
-// that happened on a page that had been in the background. When a page is
-// backgrounded, some events (e.g. paint) are delayed. Since these data points
-// can skew the mean, they should not be mixed with timing events that occurred
-// in the foreground.
-bool EventOccurredInForeground(base::TimeDelta event,
-                               const PageLoadExtraInfo& info);
+// Returns true if:
+// - We have timing information for the event.
+// - The page load started while the page was in the foreground.
+// - The event occurred prior to the page being moved to the background.
+// When a page is backgrounded, some events (e.g. paint) are delayed. Since
+// these data points can skew the mean, they should not be mixed with timing
+// events that occurred in the foreground.
+bool WasStartedInForegroundEventInForeground(base::TimeDelta event,
+                                             const PageLoadExtraInfo& info);
 
 }  // namespace page_load_metrics