Add hook_farm_asset_property() for modules to declare the properties they manage.

modules/farm/farm_asset/farm_asset_property/farm_asset_property.api.php

@@ -0,0 +1,40 @@
+<?php
+
+/**
+ * @file
+ * Hooks provided by farm_asset_property.
+ *
+ * This file contains no working PHP code; it exists to provide additional
+ * documentation for doxygen as well as to document hooks in the standard
+ * Drupal manner.
+ */
+
+/**
+ * @defgroup farm_asset_property Farm asset property module integrations.
+ *
+ * Module integrations with the farm_asset_property module.
+ */
+
+/**
+ * @defgroup farm_asset_property_hooks Farm asset property's hooks
+ * @{
+ * Hooks that can be implemented by other modules in order to extend farm_asset_property.
+ */
+
+/**
+ * Defines farm asset properties maintained by this module.
+ *
+ * @return array
+ *   Returns an array of farm asset property names.
+ */
+function hook_farm_asset_property() {
+  return array(
+    'farm_grazing_animal_type',
+    'farm_grazing_planned_arrival',
+    'farm_grazing_planned_departure',
+  );
+}
+
+/**
+ * @}
+ */