Mojo C++ bindings: fix a DCHECK in multiplex_router.h

mojo/public/cpp/bindings/lib/multiplex_router.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 "mojo/public/cpp/bindings/lib/multiplex_router.h"
 
 #include <stdint.h>
 
 #include <utility>
 
@@ skipping 684 matching lines @@
       RaiseErrorInNonTestingMode();
     return true;
   }
 
   InterfaceId id = message->interface_id();
   DCHECK(IsValidInterfaceId(id));
 
   bool inserted = false;
   InterfaceEndpoint* endpoint = FindOrInsertEndpoint(id, &inserted);
   if (inserted) {
-    DCHECK(!IsMasterInterfaceId(id));
-
     // Currently, it is legitimate to receive messages for an endpoint
     // that is not registered. For example, the endpoint is transferred in
     // a message that is discarded. Once we add support to specify all
     // enclosing endpoints in message header, we should be able to remove
     // this.
     UpdateEndpointStateMayRemove(endpoint, ENDPOINT_CLOSED);
 
-    control_message_proxy_.NotifyPeerEndpointClosed(id);
+    // It is also possible that this newly-inserted endpoint is the master
+    // endpoint. When the master InterfacePtr/Binding goes away, the message
+    // pipe is closed and we explicitly trigger a pipe connection error. The
+    // error updates all the endpoints, including the master endpoint, with
+    // PEER_ENDPOINT_CLOSED and removes the master endpoint from the
+    // registration. We continue to process remaining tasks in the queue, as
+    // long as there are refs keeping the router alive. If there are remaining
+    // messages for the master endpoint, we will get here.
+    if (!IsMasterInterfaceId(id))
+      control_message_proxy_.NotifyPeerEndpointClosed(id);
     return true;
   }
 
   if (endpoint->closed())
     return true;
 
   if (!endpoint->client()) {
     // We need to wait until a client is attached in order to dispatch further
     // messages.
     return false;
@@ skipping 96 matching lines @@
       *inserted = true;
   } else {
     endpoint = iter->second.get();
   }
 
   return endpoint;
 }
 
 }  // namespace internal
 }  // namespace mojo