Prevent a race condition with MidiHost IPC sending.

content/browser/media/midi_host.h

 // Copyright (c) 2013 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.
 
 #ifndef CONTENT_BROWSER_MEDIA_MIDI_HOST_H_
 #define CONTENT_BROWSER_MEDIA_MIDI_HOST_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 20 matching lines @@
 
 namespace content {
 
 class CONTENT_EXPORT MidiHost : public BrowserMessageFilter,
                                 public media::midi::MidiManagerClient {
  public:
   // Called from UI thread from the owner of this object.
   MidiHost(int renderer_process_id, media::midi::MidiManager* midi_manager);
 
   // BrowserMessageFilter implementation.
+  void OnChannelClosing() override;
   void OnDestruct() const override;
   bool OnMessageReceived(const IPC::Message& message) override;
 
   // MidiManagerClient implementation.
   void CompleteStartSession(media::midi::Result result) override;
   void AddInputPort(const media::midi::MidiPortInfo& info) override;
   void AddOutputPort(const media::midi::MidiPortInfo& info) override;
   void SetInputPortState(uint32_t port,
                          media::midi::MidiPortState state) override;
   void SetOutputPortState(uint32_t port,
@@ skipping 68 matching lines @@
 
   // Protects access to |output_port_count_|.
   base::Lock output_port_count_lock_;
 
   DISALLOW_COPY_AND_ASSIGN(MidiHost);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_MIDI_HOST_H_