Web MIDI: add dynamic MidiManager instantiation support for Linux

media/midi/midi_manager_alsa.h

 // Copyright 2014 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_ALSA_H_
 #define MEDIA_MIDI_MIDI_MANAGER_ALSA_H_
 
 #include <alsa/asoundlib.h>
 #include <stdint.h>
 
@@ skipping 355 matching lines @@
     };
   };
 
   using SourceMap = base::hash_map<int, uint32_t>;
   using OutPortMap = base::hash_map<uint32_t, int>;
   using ScopedSndSeqPtr = std::unique_ptr<snd_seq_t, SndSeqDeleter>;
   using ScopedSndMidiEventPtr =
       std::unique_ptr<snd_midi_event_t, SndMidiEventDeleter>;
 
   // An internal callback that runs on MidiSendThread.
-  void SendMidiData(uint32_t port_index, const std::vector<uint8_t>& data);
+  void SendMidiData(int instance_id,
+                    MidiManagerClient* client,
+                    uint32_t port_index,
+                    const std::vector<uint8_t>& data);
 
-  void ScheduleEventLoop();
-  void EventLoop();
+  void EventLoop(int instance_id);
   void ProcessSingleEvent(snd_seq_event_t* event, double timestamp);
   void ProcessClientStartEvent(int client_id);
   void ProcessPortStartEvent(const snd_seq_addr_t& addr);
   void ProcessClientExitEvent(const snd_seq_addr_t& addr);
   void ProcessPortExitEvent(const snd_seq_addr_t& addr);
   void ProcessUdevEvent(udev_device* dev);
   void AddCard(udev_device* dev);
   void RemoveCard(int number);
 
   // Updates port_state_ and Web MIDI state from alsa_seq_state_.
@@ skipping 50 matching lines @@
   int out_client_id_;
   int in_port_id_;
 
   // ALSA event -> MIDI coder.
   ScopedSndMidiEventPtr decoder_;
 
   // udev, for querying hardware devices.
   device::ScopedUdevPtr udev_;
   device::ScopedUdevMonitorPtr udev_monitor_;
 
-  // Threads for sending and receiving. These are initialized in the
-  // constructor, but are started at the end of StartInitialization.
-  base::Thread event_thread_;
-  base::Thread send_thread_;
+  int instance_id_;
 
   DISALLOW_COPY_AND_ASSIGN(MidiManagerAlsa);
 };
 
 }  // namespace midi
 
 #endif  // MEDIA_MIDI_MIDI_MANAGER_ALSA_H_