Mojo: Add a MessageInTransit::Swap() method and remove the "PassContents" ctor.

mojo/system/message_in_transit_queue.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 "mojo/system/message_in_transit_queue.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 
 namespace mojo {
 namespace system {
 
 MessageInTransitQueue::MessageInTransitQueue() {
 }
 
-MessageInTransitQueue::MessageInTransitQueue(PassContents,
-                                             MessageInTransitQueue* other) {
-  queue_.swap(other->queue_);
-}
-
 MessageInTransitQueue::~MessageInTransitQueue() {
   if (!IsEmpty()) {
     LOG(WARNING) << "Destroying nonempty message queue";
     Clear();
   }
 }
 
 void MessageInTransitQueue::Clear() {
   STLDeleteElements(&queue_);
 }
 
+void MessageInTransitQueue::Swap(MessageInTransitQueue* other) {
+  queue_.swap(other->queue_);
+}
+
 }  // namespace system
 }  // namespace mojo