chrome: Add out-of-line copy ctors for complex classes.

chrome/browser/memory/tab_stats.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 "build/build_config.h"
 #include "chrome/browser/memory/tab_stats.h"
 
 namespace memory {
 
 TabStats::TabStats()
     : is_app(false),
       is_internal_page(false),
       is_media(false),
       is_pinned(false),
       is_selected(false),
       is_discarded(false),
       has_form_entry(false),
       discard_count(0),
       render_process_host(nullptr),
       renderer_handle(0),
       child_process_host_id(0),
 #if defined(OS_CHROMEOS)
       oom_score(0),
 #endif
       tab_contents_id(0) {
 }
 
+TabStats::TabStats(const TabStats& other) = default;
+
 TabStats::~TabStats() {
 }
 
 }  // namespace memory