Add more out of line copy ctors for complex classes.

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() {}
 
+PageLoadTiming::PageLoadTiming(const PageLoadTiming& other) = default;
+
 PageLoadTiming::~PageLoadTiming() {}
 
 bool PageLoadTiming::operator==(const PageLoadTiming& other) const {
   return navigation_start == other.navigation_start &&
          response_start == other.response_start &&
          dom_loading == other.dom_loading &&
          dom_content_loaded_event_start ==
              other.dom_content_loaded_event_start &&
          load_event_start == other.load_event_start &&
          first_layout == other.first_layout &&
          first_paint == other.first_paint &&
          first_text_paint == other.first_text_paint &&
          first_image_paint == other.first_image_paint;
 }
 
 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();
 }
 
 }  // namespace page_load_metrics