add a default addTile() class to grid. this is only a placeholder, as it is to be implemented by subclasses.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@517 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/Grid.js

@@ -264,6 +264,20 @@ OpenLayers.Layer.Grid.prototype = Object.extend( new OpenLayers.Layer(), {
         }
     },
 
+    /**
+    * addTile gives subclasses of Grid the opportunity to create an 
+    * OpenLayer.Tile of their choosing. The implementer should initialize 
+    * the new tile and take whatever steps necessary to display it.
+    *
+    * @param {OpenLayers.Bounds} bounds
+    *
+    * @returns The added OpenLayers.Tile
+    * @type OpenLayers.Tile
+    */
+    addTile:function(bounds,position) {
+        // Should be implemented by subclasses
+    },
+
     /** @final @type String */
     CLASS_NAME: "OpenLayers.Grid"
 });