[Device Service] Add ACCELEROMETER implementation on Mac to //device/generic_sensor

device/generic_sensor/platform_sensor_accelerometer_mac.cc

+// Copyright 2017 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 "device/generic_sensor/platform_sensor_accelerometer_mac.h"
+
+#include <stdint.h>
+
+#include <cmath>
+
+#include "base/bind.h"
+#include "device/base/synchronization/shared_memory_seqlock_buffer.h"
+#include "device/generic_sensor/generic_sensor_consts.h"
+#include "device/generic_sensor/platform_sensor_provider_mac.h"
+#include "third_party/sudden_motion_sensor/sudden_motion_sensor_mac.h"
+
+namespace {
+
+constexpr double kMeanGravity = 9.80665;
+
+constexpr double kGravityThreshold = kMeanGravity * 0.01;
+
+bool IsSignificantlyDifferent(const device::SensorReading& reading1,
+                              const device::SensorReading& reading2) {
+  return (std::fabs(reading1.values[0] - reading2.values[0]) >=
+          kGravityThreshold) ||
+         (std::fabs(reading1.values[1] - reading2.values[1]) >=
+          kGravityThreshold) ||
+         (std::fabs(reading1.values[2] - reading2.values[2]) >=
+          kGravityThreshold);
+}
+
+}  // namespace
+
+namespace device {
+
+PlatformSensorAccelerometerMac::PlatformSensorAccelerometerMac(
+    mojo::ScopedSharedBufferMapping mapping,
+    PlatformSensorProvider* provider)
+    : PlatformSensor(mojom::SensorType::ACCELEROMETER,
+                     std::move(mapping),
+                     provider),
+      sudden_motion_sensor_(SuddenMotionSensor::Create()) {}
+
+PlatformSensorAccelerometerMac::~PlatformSensorAccelerometerMac() = default;
+
+mojom::ReportingMode PlatformSensorAccelerometerMac::GetReportingMode() {
+  return mojom::ReportingMode::ON_CHANGE;
+}
+
+bool PlatformSensorAccelerometerMac::CheckSensorConfiguration(
+    const PlatformSensorConfiguration& configuration) {
+  return configuration.frequency() > 0 &&
+         configuration.frequency() <=
+             mojom::SensorConfiguration::kMaxAllowedFrequency;
+}
+
+PlatformSensorConfiguration
+PlatformSensorAccelerometerMac::GetDefaultConfiguration() {
+  PlatformSensorConfiguration default_configuration;
+  default_configuration.set_frequency(kDefaultAccelerometerFrequencyHz);
+  return default_configuration;

[Reilly Grant (use Gerrit), 2017/05/13 00:33:16]

return PlatformSensorConfiguration(kDefaultAccelerometerFrequencyHz);

[juncai, 2017/05/13 00:53:49]

Done.

+}
+
+bool PlatformSensorAccelerometerMac::StartSensor(
+    const PlatformSensorConfiguration& configuration) {
+  if (!sudden_motion_sensor_)
+    return false;
+
+  float axis_value[3];
+  if (!sudden_motion_sensor_->ReadSensorValues(axis_value))
+    return false;
+
+  timer_.Start(
+      FROM_HERE,
+      base::TimeDelta::FromMicroseconds(base::Time::kMicrosecondsPerSecond /
+                                        configuration.frequency()),
+      this, &PlatformSensorAccelerometerMac::PollForData);
+
+  return true;
+}
+
+void PlatformSensorAccelerometerMac::StopSensor() {
+  timer_.Stop();
+}
+
+void PlatformSensorAccelerometerMac::PollForData() {
+  // Retrieve per-axis calibrated values.
+  float axis_value[3];
+  if (!sudden_motion_sensor_->ReadSensorValues(axis_value))
+    return;
+
+  SensorReading reading;
+  reading.timestamp = (base::TimeTicks::Now() - base::TimeTicks()).InSecondsF();
+  reading.values[0] = axis_value[0] * kMeanGravity;
+  reading.values[1] = axis_value[1] * kMeanGravity;
+  reading.values[2] = axis_value[2] * kMeanGravity;
+
+  if (IsSignificantlyDifferent(reading_, reading)) {
+    reading_ = reading;
+    UpdateSensorReading(reading, true);
+  }
+}
+
+}  // namespace device