Web MIDI: add MidiScheduler for send() with timestamp

media/midi/midi_scheduler.cc

+// 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.
+
+#include "media/midi/midi_scheduler.h"
+
+#include "base/bind.h"
+#include "base/message_loop/message_loop.h"
+#include "base/time/time.h"
+#include "media/midi/midi_manager.h"
+
+namespace media {
+
+MidiScheduler::MidiScheduler() : weak_factory_(this) {
+}
+
+MidiScheduler::~MidiScheduler() {
+}
+
+// TODO(crbug.com/467442): Use CancelableTaskTracker once it supports
+// DelayedTask.
+void MidiScheduler::PostSendDataTask(MidiManagerClient* client,
+                                     size_t length,
+                                     double timestamp,
+                                     const base::Closure& closure) {
+  DCHECK(client);
+
+  const base::Closure& weak_closure = base::Bind(
+      &MidiScheduler::InvokeClosure, weak_factory_.GetWeakPtr(), closure);
+
+  base::TimeDelta delay;
+  if (timestamp != 0.0) {
+    base::TimeTicks time_to_send =
+        base::TimeTicks() + base::TimeDelta::FromMicroseconds(
+                                timestamp * base::Time::kMicrosecondsPerSecond);
+    delay = std::max(time_to_send - base::TimeTicks::Now(), base::TimeDelta());
+  }
+  base::MessageLoop::current()->task_runner()->PostDelayedTask(
+      FROM_HERE, weak_closure, delay);
+
+  // TODO(crbug.com/467442): AccumulateMidiBytesSent should be called in
+  // InvokeClosure. But for now, we call it here since |client| may be deleted
+  // at that time.
+  client->AccumulateMidiBytesSent(length);
+}
+
+void MidiScheduler::InvokeClosure(const base::Closure& closure) {
+  closure.Run();
+}
+
+}  // namespace media