Basic vector source and layer

The vector source maintains a cache of features.  These are indexed by geometry type in anticipation of the renderer's needs.

src/ol/layer/vectorlayer.js

@@ -0,0 +1,24 @@
+goog.provide('ol.layer.VectorLayer');
+
+goog.require('ol.layer.Layer');
+goog.require('ol.source.Vector');
+
+
+
+/**
+ * @constructor
+ * @extends {ol.layer.Layer}
+ * @param {ol.layer.LayerOptions} layerOptions Layer options.
+ */
+ol.layer.VectorLayer = function(layerOptions) {
+  goog.base(this, layerOptions);
+};
+goog.inherits(ol.layer.VectorLayer, ol.layer.Layer);
+
+
+/**
+ * @return {ol.source.Vector} Source.
+ */
+ol.layer.VectorLayer.prototype.getVectorSource = function() {
+  return /** @type {ol.source.Vector} */ (this.getSource());
+};