Optional <TimeDelta> since they may be non existent.

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/optional.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;
 
 // 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.
+// If the event time delta and background time delta are equal, we still
+// consider the event to be logged in the foreground histogram since any
+// background specific handling would not yet have been applied to that event.
 bool WasStartedInForegroundEventInForeground(base::TimeDelta event,
                                              const PageLoadExtraInfo& info);
 
+bool WasStartedInForegroundOptionalEventInForeground(
+    const base::Optional<base::TimeDelta>& event,
+    const PageLoadExtraInfo& info);
+
 // Returns true if:
 // - Parse started and did not complete but the entire page load duration
 // happened in the foreground.
 // - Parse completed and happened entirely in the foreground.
 bool WasParseInForeground(base::TimeDelta parse_start,
                           base::TimeDelta parse_stop,
                           const PageLoadExtraInfo& info);
-
 }  // namespace page_load_metrics
 
 #endif  // COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_UTIL_H_