Add more out of line copy ctors for complex classes.

mojo/edk/system/request_context.cc

 // Copyright 2016 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 "mojo/edk/system/request_context.h"
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/threading/thread_local.h"
 
@@ skipping 72 matching lines @@
   return tls_context_->Get() == this;
 }
 
 RequestContext::WatchNotifyFinalizer::WatchNotifyFinalizer(
     scoped_refptr<Watcher> watcher,
     MojoResult result,
     const HandleSignalsState& state)
     : watcher(watcher), result(result), state(state) {
 }
 
+RequestContext::WatchNotifyFinalizer::WatchNotifyFinalizer(
+    const WatchNotifyFinalizer& other) = default;
+
 RequestContext::WatchNotifyFinalizer::~WatchNotifyFinalizer() {}
 
 }  // namespace edk
 }  // namespace mojo