Optional <TimeDelta> since they may be non existent.

components/page_load_metrics/browser/metrics_web_contents_observer.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_METRICS_WEB_CONTENTS_OBSERVER_H_
 #define COMPONENTS_PAGE_LOAD_METRICS_BROWSER_METRICS_WEB_CONTENTS_OBSERVER_H_
 
 #include <map>
 #include <vector>
 
@@ skipping 134 matching lines @@
   // This method returns true if this page load has been aborted with type of
   // ABORT_OTHER, and the |abort_cause_time| is within a sufficiently close
   // delta to when it was aborted. Note that only provisional loads can be
   // aborted with ABORT_OTHER. While this heuristic is coarse, it works better
   // and is simpler than other feasible methods. See https://goo.gl/WKRG98.
   bool IsLikelyProvisionalAbort(base::TimeTicks abort_cause_time);
 
   bool MatchesOriginalNavigation(content::NavigationHandle* navigation_handle);
 
  private:
-  PageLoadExtraInfo GetPageLoadMetricsInfo();
+  PageLoadExtraInfo ComputePageLoadExtraInfo();
 
   // Only valid to call post-commit.
   const GURL& committed_url();
 
   void UpdateAbortInternal(UserAbortType abort_type,
                            base::TimeTicks timestamp);
 
   // If |final_navigation| is null, then this is an "unparented" abort chain,
   // and represents a sequence of provisional aborts that never ends with a
   // committed load.
@@ skipping 116 matching lines @@
   std::vector<scoped_ptr<PageLoadTracker>> aborted_provisional_loads_;
 
   scoped_ptr<PageLoadTracker> committed_load_;
 
   DISALLOW_COPY_AND_ASSIGN(MetricsWebContentsObserver);
 };
 
 }  // namespace page_load_metrics
 
 #endif  // COMPONENTS_PAGE_LOAD_METRICS_BROWSER_METRICS_WEB_CONTENTS_OBSERVER_H_