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

device/udev_linux/udev.h

Index: device/udev_linux/udev.h
diff --git a/device/udev_linux/udev.h b/device/udev_linux/udev.h
index 2bb8df2695f1511b154b8209f474831049144052..3039aa269b1e929f44cdb6a58ce641a05d3e0a24 100644
--- a/device/udev_linux/udev.h
+++ b/device/udev_linux/udev.h
@@ -9,6 +9,8 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
+#include <string>
+
 #if !defined(USE_UDEV)
 #error "USE_UDEV not defined"
 #endif
@@ -72,6 +74,11 @@ void udev_set_log_fn(
 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_