Fix possible multiple calls to MidiManager::StartInitialization() in StartSession()

media/midi/midi_manager.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 MEDIA_MIDI_MIDI_MANAGER_H_
 #define MEDIA_MIDI_MIDI_MANAGER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 157 matching lines @@
 
   size_t clients_size_for_testing() const { return clients_.size(); }
   size_t pending_clients_size_for_testing() const {
     return pending_clients_.size();
   }
 
   const MidiPortInfoList& input_ports() const { return input_ports_; }
   const MidiPortInfoList& output_ports() const { return output_ports_; }
 
  private:
+  enum class InitializationState {
+    NOT_STARTED,
+    STARTED,
+    COMPLETED,
+  };
+
   void CompleteInitializationInternal(mojom::Result result);
   void AddInitialPorts(MidiManagerClient* client);
   void ShutdownOnSessionThread();
 
   // Keeps track of all clients who wish to receive MIDI data.
   typedef std::set<MidiManagerClient*> ClientSet;
   ClientSet clients_;
 
   // Keeps track of all clients who are waiting for CompleteStartSession().
   ClientSet pending_clients_;
 
   // Keeps a SingleThreadTaskRunner of the thread that calls StartSession in
   // order to invoke CompleteStartSession() on the thread.
   scoped_refptr<base::SingleThreadTaskRunner> session_thread_runner_;
 
-  // Keeps true if platform dependent initialization is already completed.
-  bool initialized_;
+  // Tracks platform dependent initialization state.
+  InitializationState initialization_state_;
 
   // Keeps false until Finalize() is called.
   bool finalized_;
 
   // Keeps the platform dependent initialization result if initialization is
   // completed. Otherwise keeps mojom::Result::NOT_INITIALIZED.
   mojom::Result result_;
 
   // Keeps all MidiPortInfo.
   MidiPortInfoList input_ports_;
   MidiPortInfoList output_ports_;
 
   // Protects access to |clients_|, |pending_clients_|,
-  // |session_thread_runner_|, |initialized_|, |finalize_|, |result_|,
+  // |session_thread_runner_|, |initialization_state_|, |finalize_|, |result_|,
   // |input_ports_| and |output_ports_|.
   base::Lock lock_;
 
   DISALLOW_COPY_AND_ASSIGN(MidiManager);
 };
 
 }  // namespace midi
 
 #endif  // MEDIA_MIDI_MIDI_MANAGER_H_