Clean up HID backend and API.

device/hid/hid_utils_mac.h

-// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Copyright 2014 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_HID_HID_UTILS_MAC_H_
 #define DEVICE_HID_HID_UTILS_MAC_H_
 
-#include "base/callback.h"
-#include "base/memory/ref_counted.h"
+#include <CoreFoundation/CoreFoundation.h>
+#include <IOKit/hid/IOHIDManager.h>
+#include <stdint.h>
 
-#include <IOKit/hid/IOHIDManager.h>
+#include <string>
 
 namespace device {
 
-bool GetHidIntProperty(IOHIDDeviceRef device, CFStringRef key, int32_t* result);
+int32_t GetHidIntProperty(IOHIDDeviceRef device, CFStringRef key);
 
-bool GetHidStringProperty(IOHIDDeviceRef device,
-                       CFStringRef key,
-                       std::string* result);
+std::string GetHidStringProperty(IOHIDDeviceRef device, CFStringRef key);
+
+bool TryGetHidIntProperty(IOHIDDeviceRef device,
+                          CFStringRef key,
+                          int32_t* result);
+
+bool TryGetHidStringProperty(IOHIDDeviceRef device,
+                             CFStringRef key,
+                             std::string* result);
 
 }  // namespace device
 
 #endif  // DEVICE_HID_HID_UTILS_MAC_H_