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

components/dom_distiller/core/article_distillation_update.cc

 // Copyright 2014 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/dom_distiller/core/article_distillation_update.h"
 
 #include "base/logging.h"
 
 namespace dom_distiller {
 
 ArticleDistillationUpdate::ArticleDistillationUpdate(
     const std::vector<scoped_refptr<RefCountedPageProto> >& pages,
     bool has_next_page,
     bool has_prev_page)
     : has_next_page_(has_next_page),
       has_prev_page_(has_prev_page),
       pages_(pages) {}
 
+ArticleDistillationUpdate::ArticleDistillationUpdate(
+    const ArticleDistillationUpdate& other) = default;
+
 ArticleDistillationUpdate::~ArticleDistillationUpdate() {}
 
 const DistilledPageProto& ArticleDistillationUpdate::GetDistilledPage(
     size_t index) const {
   DCHECK_GT(pages_.size(), index);
   return pages_[index]->data;
 }
 
 }  // namespace dom_distiller