Determine routing ID before potentially invalidating the frame

extensions/renderer/messaging_bindings.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 "extensions/renderer/messaging_bindings.h"
 
 #include <stdint.h>
 
 #include <map>
 #include <string>
@@ skipping 431 matching lines @@
 
 // static
 void MessagingBindings::DispatchOnConnect(
     const ScriptContextSet& context_set,
     int target_port_id,
     const std::string& channel_name,
     const ExtensionMsg_TabConnectionInfo& source,
     const ExtensionMsg_ExternalConnectionInfo& info,
     const std::string& tls_channel_id,
     content::RenderFrame* restrict_to_render_frame) {
+  int routing_id = restrict_to_render_frame
+                       ? restrict_to_render_frame->GetRoutingID()
+                       : MSG_ROUTING_NONE;
   bool port_created = false;
   context_set.ForEach(
       info.target_id, restrict_to_render_frame,
       base::Bind(&DispatchOnConnectToScriptContext, target_port_id,
                  channel_name, &source, info, tls_channel_id, &port_created));

[Devlin, 2016/05/02 13:57:08]

Let's add a comment like
// Note: |restrict_to_render_frame| may be deleted here!
so that we don't (or at least, are less likely to) repeat the same mistake
later.

 
-  int routing_id = restrict_to_render_frame
-                       ? restrict_to_render_frame->GetRoutingID()
-                       : MSG_ROUTING_NONE;
   if (port_created) {
     content::RenderThread::Get()->Send(
         new ExtensionHostMsg_OpenMessagePort(routing_id, target_port_id));
   } else {
     content::RenderThread::Get()->Send(new ExtensionHostMsg_CloseMessagePort(
         routing_id, target_port_id, false));
   }
 }
 
 // static
@@ skipping 12 matching lines @@
     const ScriptContextSet& context_set,
     int port_id,
     const std::string& error_message,
     content::RenderFrame* restrict_to_render_frame) {
   context_set.ForEach(
       restrict_to_render_frame,
       base::Bind(&DispatchOnDisconnectToScriptContext, port_id, error_message));
 }
 
 }  // namespace extensions