Don't log background navigations in StaleWhileRevalidateExperiment histograms

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 b5a569867db22bd488ace4ac2009a0f5f3b4a872..0865bfa74aba86297d01cb89c8a785da9b31257b 100644
--- a/components/page_load_metrics/browser/page_load_metrics_util.h
+++ b/components/page_load_metrics/browser/page_load_metrics_util.h
@@ -15,6 +15,7 @@
 
 namespace page_load_metrics {
 
+struct PageLoadExtraInfo;
 struct PageLoadTiming;
 
 // Get the time of the first 'contentful' paint. A contentful paint is a paint
@@ -22,6 +23,14 @@ struct PageLoadTiming;
 // Painting of a background color is not considered 'contentful'.
 base::TimeDelta GetFirstContentfulPaint(const PageLoadTiming& timing);
 
+// 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(const base::TimeDelta& event,
+                               const PageLoadExtraInfo& info);
+
 }  // namespace page_load_metrics
 
 #endif  // COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_UTIL_H_