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

components/device_event_log/device_event_log_impl.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/device_event_log/device_event_log_impl.h"
 
 #include <cmath>
 #include <list>
 #include <set>
 
@@ skipping 381 matching lines @@
       count(1) {
   if (filedesc) {
     file = filedesc;
     size_t last_slash_pos = file.find_last_of("\\/");
     if (last_slash_pos != std::string::npos) {
       file.erase(0, last_slash_pos + 1);
     }
   }
 }
 
+DeviceEventLogImpl::LogEntry::LogEntry(const LogEntry& other) = default;
+
 }  // namespace device_event_log