Optional <TimeDelta> since they may be non existent.

components/page_load_metrics/browser/page_load_metrics_observer.cc

 // 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.
 
 #include "components/page_load_metrics/browser/page_load_metrics_observer.h"
 
 namespace page_load_metrics {
 
-PageLoadExtraInfo::PageLoadExtraInfo(base::TimeDelta first_background_time,
-                                     base::TimeDelta first_foreground_time,
-                                     bool started_in_foreground,
-                                     const GURL& committed_url,
-                                     base::TimeDelta time_to_commit,
-                                     UserAbortType abort_type,
-                                     base::TimeDelta time_to_abort,
-                                     const PageLoadMetadata& metadata)
+PageLoadExtraInfo::PageLoadExtraInfo(
+    const base::Optional<base::TimeDelta>& first_background_time,
+    const base::Optional<base::TimeDelta>& first_foreground_time,
+    bool started_in_foreground,
+    const GURL& committed_url,
+    const base::Optional<base::TimeDelta>& time_to_commit,
+    UserAbortType abort_type,
+    const base::Optional<base::TimeDelta>& time_to_abort,
+    const PageLoadMetadata& metadata)
     : first_background_time(first_background_time),
       first_foreground_time(first_foreground_time),
       started_in_foreground(started_in_foreground),
       committed_url(committed_url),
       time_to_commit(time_to_commit),
       abort_type(abort_type),
       time_to_abort(time_to_abort),
       metadata(metadata) {}
 
 PageLoadExtraInfo::PageLoadExtraInfo(const PageLoadExtraInfo& other) = default;
 
+// Using Optional <T> for the fields made clang complaint about not having

[Charlie Harrison, 2016/05/19 18:20:49]

Suggestion: This comment isn't that useful. You can remove it if you want.

[shivanisha, 2016/05/23 15:06:43]

removed

+// an explicit out-of-line destructor
+PageLoadExtraInfo::~PageLoadExtraInfo() {}
 }  // namespace page_load_metrics