Move GetUdevDevicePropertyValue from components/storage_monitor to device/udev_linux and rename to …

device/udev_linux/udev.h

 // 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_UDEV_LINUX_UDEV_H_
 #define DEVICE_UDEV_LINUX_UDEV_H_
 
 #include <stdarg.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 
+#include <string>
+
 #if !defined(USE_UDEV)
 #error "USE_UDEV not defined"
 #endif
 
 // Adapted from libudev.h.
 #define udev_list_entry_foreach(list_entry, first_entry) \
   for (list_entry = first_entry; list_entry != NULL;     \
        list_entry = ::device::udev_list_entry_get_next(list_entry))
 
 // Forward declarations of opaque structs.
@@ skipping 43 matching lines @@
 udev_device* udev_monitor_receive_device(udev_monitor* udev_monitor);
 void udev_monitor_unref(udev_monitor* udev_monitor);
 udev* udev_new();
 void udev_set_log_fn(
     struct udev* udev,
     void (*log_fn)(struct udev* udev, int priority, const char* file, int line,
                    const char* fn, const char* format, va_list args));
 void udev_set_log_priority(struct udev* udev, int priority);
 void udev_unref(udev* udev);
 
+// Calls udev_device_get_property_value() and replaces missing values with
+// the empty string.
+std::string UdevDeviceGetPropertyValue(udev_device* udev_device,
+                                       const char* key);
+
 }  // namespace device
 
 #endif  // DEVICE_UDEV_LINUX_UDEV_H_