[sensors] [mac] Implement ambient light sensor for macOS

device/sensors/public/cpp/device_util_mac.h

Index: device/sensors/public/cpp/device_util_mac.h
diff --git a/device/sensors/public/cpp/device_util_mac.h b/device/sensors/public/cpp/device_util_mac.h
new file mode 100644
index 0000000000000000000000000000000000000000..82c728af5d4e967b3cea3ba8f8f0807ef49d1495
--- /dev/null
+++ b/device/sensors/public/cpp/device_util_mac.h
@@ -0,0 +1,18 @@
+// 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 DEVICE_SENSORS_PUBLIC_CPP_DEVICE_UTIL_MAC_H_
+#define DEVICE_SENSORS_PUBLIC_CPP_DEVICE_UTIL_MAC_H_
+
+#include <stdint.h>
+
+namespace device {
+
+// Convert the value returned by the ambient light LMU sensor on Mac
+// hardware to a lux value.
+double LMUvalueToLux(uint64_t raw_value);
+
+}  // namespace device
+
+#endif  // DEVICE_SENSORS_PUBLIC_CPP_DEVICE_UTIL_MAC_H_