Update PageLoadTiming to use base::Optional

components/page_load_metrics/common/page_load_timing.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/common/page_load_timing.h"
 
 namespace page_load_metrics {
 
 PageLoadTiming::PageLoadTiming() {}
 
@@ skipping 13 matching lines @@
          first_text_paint == other.first_text_paint &&
          first_image_paint == other.first_image_paint &&
          parse_start == other.parse_start && parse_stop == other.parse_stop &&
          parse_blocked_on_script_load_duration ==
              other.parse_blocked_on_script_load_duration &&
          parse_blocked_on_script_load_from_document_write_duration ==
              other.parse_blocked_on_script_load_from_document_write_duration;
 }
 
 bool PageLoadTiming::IsEmpty() const {
-  return navigation_start.is_null() && response_start.is_zero() &&
-         dom_loading.is_zero() && dom_content_loaded_event_start.is_zero() &&
-         load_event_start.is_zero() && first_layout.is_zero() &&
-         first_paint.is_zero() && first_text_paint.is_zero() &&
-         first_image_paint.is_zero() && parse_start.is_zero() &&
-         parse_stop.is_zero() &&
-         parse_blocked_on_script_load_duration.is_zero() &&
-         parse_blocked_on_script_load_from_document_write_duration.is_zero();
+  return navigation_start.is_null() && !response_start && !dom_loading &&
+         !dom_content_loaded_event_start && !load_event_start &&
+         !first_layout && !first_paint && !first_text_paint &&
+         !first_image_paint && !parse_start && !parse_stop &&
+         !parse_blocked_on_script_load_duration &&
+         !parse_blocked_on_script_load_from_document_write_duration;
 }
 
 PageLoadMetadata::PageLoadMetadata() {}
 
 bool PageLoadMetadata::operator==(const PageLoadMetadata& other) const {
   return behavior_flags == other.behavior_flags;
 }
 
 }  // namespace page_load_metrics