Web MIDI: add dynamic MidiManager instantiation support for Linux

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 27e24f92cd9c86937622e5f311977d5e59be2252..cea56b0d75b2591c3a08d9c193618372a5273760 100644
--- a/media/midi/midi_manager.h
+++ b/media/midi/midi_manager.h
@@ -25,6 +25,8 @@ class SingleThreadTaskRunner;
 
 namespace midi {
 
+class MidiService;
+
 // A MidiManagerClient registers with the MidiManager to receive MIDI data.
 // See MidiManager::RequestAccess() and MidiManager::ReleaseAccess()
 // for details.
@@ -73,19 +75,24 @@ class MIDI_EXPORT MidiManagerClient {
 };
 
 // Manages access to all MIDI hardware.
+// *** Note ***: If dynamic instantiation feature is enabled, all MidiManager
+// methods will be called on Chrome_IOThread. See comments on Shutdown() too.
 class MIDI_EXPORT MidiManager {
  public:
   static const size_t kMaxPendingClientCount = 128;
 
-  MidiManager();
+  explicit MidiManager(MidiService* service);
   virtual ~MidiManager();
 
   // The constructor and the destructor will be called on the CrBrowserMain
   // thread.
-  static MidiManager* Create();
+  static MidiManager* Create(MidiService* service);
 
   // Called on the CrBrowserMain thread to notify the Chrome_IOThread will stop
   // and the instance will be destructed on the CrBrowserMain thread soon.
+  // *** Note ***: If dynamic instantiation feature is enabled, MidiService
+  // calls this on Chrome_IOThread and ShutdownOnSessionThread() will be called
+  // synchronously so that MidiService can destruct MidiManager synchronously.
   void Shutdown();
 
   // A client calls StartSession() to receive and send MIDI data.
@@ -174,6 +181,7 @@ class MIDI_EXPORT MidiManager {
 
   const MidiPortInfoList& input_ports() const { return input_ports_; }
   const MidiPortInfoList& output_ports() const { return output_ports_; }
+  MidiService* service() { return service_; }
 
  private:
   enum class InitializationState {
@@ -216,6 +224,9 @@ class MIDI_EXPORT MidiManager {
   // |input_ports_| and |output_ports_|.
   base::Lock lock_;
 
+  // MidiService outlives MidiManager.
+  MidiService* const service_;
+
   DISALLOW_COPY_AND_ASSIGN(MidiManager);
 };