Web MIDI: introduce MidiManager::Shutdown to shutdown gracefully

media/midi/midi_manager.h

Index: media/midi/midi_manager.h
diff --git a/media/midi/midi_manager.h b/media/midi/midi_manager.h
index 957c84d427f0dc85b291cd6b9cee188067dca5d7..8870fd999affc72a09b03cafdd845017fb270e2a 100644
--- a/media/midi/midi_manager.h
+++ b/media/midi/midi_manager.h
@@ -75,6 +75,10 @@ class MIDI_EXPORT MidiManager {
   // thread.
   static MidiManager* Create();
 
+  // Called on the CrBrowserMain thread to notify the Chrome_IOThread will stop
+  // and the instance will be destructed on the CrBrowserMain thread soon.
+  void Shutdown();
+
   // A client calls StartSession() to receive and send MIDI data.
   // If the session is ready to start, the MIDI system is lazily initialized
   // and the client is registered to receive MIDI data.
@@ -119,6 +123,12 @@ class MIDI_EXPORT MidiManager {
   // |result| should be Result::OK on success, otherwise a proper Result.
   virtual void StartInitialization();
 
+  // Finalizes the platform dependent MIDI system. Called on Chrome_IOThread
+  // thread and the thread will stop immediately after this call.
+  // Platform dependent resources that were allocated on the Chrome_IOThread
+  // should be disposed inside this method.
+  virtual void Finalize() {}
+
   // Called from a platform dependent implementation of StartInitialization().
   // It invokes CompleteInitializationInternal() on the thread that calls
   // StartSession() and distributes |result| to MIDIManagerClient objects in
@@ -154,6 +164,7 @@ class MIDI_EXPORT MidiManager {
  private:
   void CompleteInitializationInternal(Result result);
   void AddInitialPorts(MidiManagerClient* client);
+  void ShutdownOnSessionThread();
 
   // Keeps track of all clients who wish to receive MIDI data.
   typedef std::set<MidiManagerClient*> ClientSet;
@@ -169,6 +180,9 @@ class MIDI_EXPORT MidiManager {
   // Keeps true if platform dependent initialization is already completed.
   bool initialized_;
 
+  // Keeps false until Finalize() is called.
+  bool finalized_;
+
   // Keeps the platform dependent initialization result if initialization is
   // completed. Otherwise keeps Result::NOT_INITIALIZED.
   Result result_;
@@ -178,7 +192,7 @@ class MIDI_EXPORT MidiManager {
   MidiPortInfoList output_ports_;
 
   // Protects access to |clients_|, |pending_clients_|, |initialized_|,
-  // |result_|, |input_ports_| and |output_ports_|.
+  // |finalize_|, |result_|, |input_ports_| and |output_ports_|.
   base::Lock lock_;
 
   DISALLOW_COPY_AND_ASSIGN(MidiManager);