Ignore certain messages in plugin broker process if they are not sent by the

content/browser/ppapi_plugin_process_host.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 "content/browser/ppapi_plugin_process_host.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <utility>
@@ skipping 453 matching lines @@
       cmd_line,
       true);
   return true;
 }
 
 void PpapiPluginProcessHost::RequestPluginChannel(Client* client) {
   base::ProcessHandle process_handle;
   int renderer_child_id;
   client->GetPpapiChannelInfo(&process_handle, &renderer_child_id);
 
-  base::ProcessId process_id = (process_handle == base::kNullProcessHandle) ?
-      0 : base::GetProcId(process_handle);
+  base::ProcessId process_id = base::kNullProcessId;
+  if (process_handle != base::kNullProcessHandle) {
+    // This channel is not used by the browser itself.
+    process_id = base::GetProcId(process_handle);
+    CHECK_NE(base::kNullProcessId, process_id);
+  }
 
   // We can't send any sync messages from the browser because it might lead to
   // a hang. See the similar code in PluginProcessHost for more description.
   PpapiMsg_CreateChannel* msg = new PpapiMsg_CreateChannel(
       process_id, renderer_child_id, client->OffTheRecord());
   msg->set_unblock(true);
   if (Send(msg)) {
     sent_requests_.push(client);
   } else {
     client->OnPpapiChannelOpened(IPC::ChannelHandle(), base::kNullProcessId, 0);
@@ skipping 72 matching lines @@
   // sent_requests_ queue should be the one that the plugin just created.
   Client* client = sent_requests_.front();
   sent_requests_.pop();
 
   const ChildProcessData& data = process_->GetData();
   client->OnPpapiChannelOpened(channel_handle, base::GetProcId(data.handle),
                                data.id);
 }
 
 }  // namespace content