Add RELATIVE_ORIENTATION sensor implementation on macOS to //device/generic_sensor

device/generic_sensor/public/cpp/sensor_shared_buffer_reader.cc

Index: device/generic_sensor/public/cpp/sensor_shared_buffer_reader.cc
diff --git a/device/generic_sensor/public/cpp/sensor_shared_buffer_reader.cc b/device/generic_sensor/public/cpp/sensor_shared_buffer_reader.cc
new file mode 100644
index 0000000000000000000000000000000000000000..6dadf92a83feb3aac7b99c20da52ab3616b36ec0
--- /dev/null
+++ b/device/generic_sensor/public/cpp/sensor_shared_buffer_reader.cc
@@ -0,0 +1,44 @@
+// 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/public/cpp/sensor_shared_buffer_reader.h"
+
+#include "device/base/synchronization/shared_memory_seqlock_buffer.h"
+#include "device/generic_sensor/public/cpp/sensor_reading.h"
+
+namespace {
+
+constexpr int kMaxReadAttemptsCount = 10;
+
+}  // namespace
+
+namespace device {
+
+SensorSharedBufferReader::SensorSharedBufferReader(
+    const SensorReadingSharedBuffer* buffer)
+    : buffer_(buffer) {}
+
+SensorSharedBufferReader::~SensorSharedBufferReader() = default;
+
+bool SensorSharedBufferReader::GetSensorReading(SensorReading* result) {
+  int read_attempts = 0;
+  while (!TryReadFromBuffer(result)) {
+    if (++read_attempts == kMaxReadAttemptsCount)
+      return false;
+  }
+
+  return true;
+}
+
+bool SensorSharedBufferReader::TryReadFromBuffer(SensorReading* result) {
+  const OneWriterSeqLock& seqlock = buffer_->seqlock.value();
+  auto version = seqlock.ReadBegin();
+  auto reading_data = buffer_->reading;
+  if (seqlock.ReadRetry(version))
+    return false;
+  *result = reading_data;
+  return true;
+}
+
+}  // namespace device