Add missing requires

Without explicit requires, it is possible that a build would exclude ol.js.

src/ol/renderer/webgl/webglmaprenderer.js

@@ -13,6 +13,7 @@ goog.require('goog.log.Logger');
 goog.require('goog.object');
 goog.require('goog.style');
 goog.require('goog.webgl');
+goog.require('ol');
 goog.require('ol.Tile');
 goog.require('ol.css');
 goog.require('ol.dom');