Don't log background navigations in StaleWhileRevalidateExperiment histograms

components/page_load_metrics/browser/page_load_metrics_util.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_UTIL_H_
 #define COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_UTIL_H_
 
 #include "base/metrics/histogram_macros.h"
 #include "base/time/time.h"
 
 #define PAGE_LOAD_HISTOGRAM(name, sample)                           \
   UMA_HISTOGRAM_CUSTOM_TIMES(name, sample,                          \
                              base::TimeDelta::FromMilliseconds(10), \
                              base::TimeDelta::FromMinutes(10), 100)
 
 namespace page_load_metrics {
 
+struct PageLoadExtraInfo;
 struct PageLoadTiming;
 
 // Get the time of the first 'contentful' paint. A contentful paint is a paint
 // that includes content of some kind (for example, text or image content).
 // 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_