Web MIDI: add MidiScheduler for send() with timestamp

media/midi/midi_scheduler.h

+// Copyright 2015 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_SCHEDULER_H_
+#define MEDIA_MIDI_MIDI_SCHEDULER_H_
+
+#include "base/callback.h"
+#include "base/memory/weak_ptr.h"
+
+namespace media {
+
+class MidiManagerClient;
+
+// TODO(crbug.com/467442): Make tasks cancelable per client.
+class MidiScheduler final {
+ public:
+  MidiScheduler();
+  ~MidiScheduler();
+
+  // Post |closure| to the current message loop safely. The |closure| will not
+  // be invoked after MidiScheduler is deleted. AccumulateMidiBytesSent() of
+  // |client| is called internally.
+  void PostSendDataTask(MidiManagerClient* client,
+                        size_t length,
+                        double timestamp,
+                        const base::Closure& closure);
+
+ private:
+  void InvokeClosure(const base::Closure& closure);
+
+  base::WeakPtrFactory<MidiScheduler> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(MidiScheduler);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_MIDI_MIDI_SCHEDULER_H_