[Device Service] Add RELATIVE_ORIENTATION sensor type to //device/generic_sensor

device/generic_sensor/platform_sensor_accelerometer_mac.cc

Index: device/generic_sensor/platform_sensor_accelerometer_mac.cc
diff --git a/device/generic_sensor/platform_sensor_accelerometer_mac.cc b/device/generic_sensor/platform_sensor_accelerometer_mac.cc
new file mode 100644
index 0000000000000000000000000000000000000000..6914548ea6a2289e5f09aa57f13ef9042f1c9325
--- /dev/null
+++ b/device/generic_sensor/platform_sensor_accelerometer_mac.cc
@@ -0,0 +1,81 @@
+// 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 "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 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;

[Mikhail, 2017/05/03 07:47:46]

so, does the accelerometer give updated values only when the device is actually
moving? what values does it give when the device is still?

[juncai, 2017/05/03 17:39:18]

Yes. When the device is still, the values are 0 for x, y, and z-axis. 

[juncai, 2017/05/03 18:13:03]

The reporting mode for Accelerometer is the same as Ambient Light on Mac. I will
have a follow-up CL to only update the blink side when the accelerometer value
changes.

[shalamov, 2017/05/04 06:53:46]

Accelerometer in rest should provide 9.8 ms2 acceleration (length of vector).
If you get all 0s, then it is mojom::SensorType::LINEAR_ACCELERATION sensor.

[juncai, 2017/05/04 17:51:09]

Bug filed:
https://bugs.chromium.org/p/chromium/issues/detail?id=718460
I will do this in a follow-up CL.

[juncai, 2017/05/04 17:51:09]

Sorry for the confusion. I did some further reading and found that when the
device is still, the value on z-axis is 9.8 instead of 0.

+}
+
+bool PlatformSensorAccelerometerMac::CheckSensorConfiguration(
+    const PlatformSensorConfiguration& configuration) {
+  return configuration.frequency() > 0 &&
+         configuration.frequency() <=
+             mojom::SensorConfiguration::kMaxAllowedFrequency;

[dcheng, 2017/05/03 20:58:53]

Is 60Hz actually OK? My understanding is there are some practical attacks to
inferring passwords at high enough sampling rates from the accelerometer: see
http://www.hotmobile.org/2012/papers/HotMobile12-final42.pdf for example.

+}
+
+PlatformSensorConfiguration
+PlatformSensorAccelerometerMac::GetDefaultConfiguration() {
+  PlatformSensorConfiguration default_configuration;
+  default_configuration.set_frequency(kDefaultAccelerometerFrequencyHz);
+  return default_configuration;
+}
+
+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];
+  reading.values[1] = axis_value[1];
+  reading.values[2] = axis_value[2];
+  UpdateSensorReading(reading, true);
+}
+
+}  // namespace device