[Sensors] Align sensor reading updates and 'onchange' notification with rAF.

third_party/WebKit/Source/modules/sensor/SensorUpdateNotifier.h

+// Copyright 2016 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 SensorUpdateNotifier_h
+#define SensorUpdateNotifier_h
+
+#include "device/generic_sensor/public/interfaces/sensor_provider.mojom-blink.h"
+#include "wtf/Functional.h"
+
+namespace blink {
+
+// This class encapsulates sensor reading update notification logic:
+// the callback is invoked after client calls 'onSensorReadingChanged()'
+// however considering the given sample frequency.
+class SensorUpdateNotifier {
+ public:
+  static std::unique_ptr<SensorUpdateNotifier> create(
+      double frequency,
+      std::unique_ptr<Function<void()>>,
+      device::mojom::blink::ReportingMode);
+
+  // Please see SensorProxy::Observer comments explaining
+  // the |timestamp| argument.
+  virtual void onSensorReadingChanged(double timestamp) = 0;
+  virtual void cancelPendingNotifications() = 0;
+  virtual ~SensorUpdateNotifier() {}
+
+ protected:
+  SensorUpdateNotifier(double period, std::unique_ptr<Function<void()>>);
+
+  double m_period;
+  std::unique_ptr<Function<void()>> m_func;
+  double m_lastTimestamp;
+};
+
+}  // namespace blink
+
+#endif  // SensorUpdateNotifier_h