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

components/drive/file_system_interface.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/drive/file_system_interface.h"
 
 namespace drive {
 
 MetadataSearchResult::MetadataSearchResult(
     const base::FilePath& path,
     bool is_directory,
     const std::string& highlighted_base_name,
     const std::string& md5)
     : path(path),
       is_directory(is_directory),
       highlighted_base_name(highlighted_base_name),
       md5(md5) {
 }
 
+MetadataSearchResult::MetadataSearchResult(const MetadataSearchResult& other) =
+    default;
+
 }  // namespace drive