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

ipc/attachment_broker.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 "ipc/attachment_broker.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/location.h"
@@ skipping 120 matching lines @@
                            });
     if (it == observers_.end())
       return;
     observer = it->observer;
   }
 
   observer->ReceivedBrokerableAttachmentWithId(id);
 }
 
 AttachmentBroker::ObserverInfo::ObserverInfo() {}
+AttachmentBroker::ObserverInfo::ObserverInfo(const ObserverInfo& other) =
+    default;
 AttachmentBroker::ObserverInfo::~ObserverInfo() {}
 
 }  // namespace IPC