Make sure channel-associated interface pointers are always safe to call.

ipc/ipc_sync_message_filter.cc

 // Copyright (c) 2012 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/ipc_sync_message_filter.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
@@ skipping 258 matching lines @@
   // message loop is destroyed. Since that destruction indicates shutdown
   // anyway, we manually signal the shutdown event in this case.
   shutdown_mojo_event_.Signal();
 }
 
 void SyncMessageFilter::GetGenericRemoteAssociatedInterface(
     const std::string& interface_name,
     mojo::ScopedInterfaceEndpointHandle handle) {
   base::AutoLock auto_lock(lock_);
   DCHECK(io_task_runner_ && io_task_runner_->BelongsToCurrentThread());
-  if (!channel_)
+  if (!channel_) {
+    // Attach the associated interface to a disconnected pipe, so that the
+    // associated interface pointer can be used to make calls (which are
+    // dropped).
+    mojo::GetIsolatedInterface(std::move(handle));
     return;
+  }
 
   Channel::AssociatedInterfaceSupport* support =
       channel_->GetAssociatedInterfaceSupport();
   support->GetGenericRemoteAssociatedInterface(
       interface_name, std::move(handle));
 }
 
 }  // namespace IPC