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..f3e6260fc04ea648c770255046cc04628444a9e1 100644
--- a/components/page_load_metrics/browser/page_load_metrics_util.h
+++ b/components/page_load_metrics/browser/page_load_metrics_util.h
@@ -22,6 +22,14 @@ 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 after the page was backgrounded. When a page is backgrounded,
+// the priority is lowered, and the load timing events no longer reflect the

[Charlie Harrison, 2015/12/08 20:26:21]

I don't know if the priority is always lowered. rdsmith@ might know more. I
would also add that some events (e.g. paint) are delayed until foreground, which
is the root cause of many long tailed histograms.

[Adam Rice, 2015/12/09 06:29:00]

I reworded the comment. PTAL.

+// user experience. 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 base::TimeDelta& first_background);
+
 }  // namespace page_load_metrics
 
 #endif  // COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_UTIL_H_