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

mojo/system/message_in_transit_queue.cc

Index: mojo/system/message_in_transit_queue.cc
diff --git a/mojo/system/message_in_transit_queue.cc b/mojo/system/message_in_transit_queue.cc
index 48f77799e073757770489da943738a9e75b16b56..1ad5ecf0f68a2200c051964614021d25fd886926 100644
--- a/mojo/system/message_in_transit_queue.cc
+++ b/mojo/system/message_in_transit_queue.cc
@@ -13,11 +13,6 @@ namespace system {
 MessageInTransitQueue::MessageInTransitQueue() {
 }
 
-MessageInTransitQueue::MessageInTransitQueue(PassContents,
-                                             MessageInTransitQueue* other) {
-  queue_.swap(other->queue_);
-}
-
 MessageInTransitQueue::~MessageInTransitQueue() {
   if (!IsEmpty()) {
     LOG(WARNING) << "Destroying nonempty message queue";
@@ -29,5 +24,9 @@ void MessageInTransitQueue::Clear() {
   STLDeleteElements(&queue_);
 }
 
+void MessageInTransitQueue::Swap(MessageInTransitQueue* other) {
+  queue_.swap(other->queue_);
+}
+
 }  // namespace system
 }  // namespace mojo