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

device/base/device_util_mac.h

Index: device/base/device_util_mac.h
diff --git a/device/base/device_util_mac.h b/device/base/device_util_mac.h
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index 0000000000000000000000000000000000000000..55511bf373d0bdeb3bc98c617b0e96f3d06288a0
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+++ b/device/base/device_util_mac.h
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+// 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_BASE_DEVICE_UTIL_MAC_H_
+#define DEVICE_BASE_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_BASE_DEVICE_UTIL_MAC_H_