add an ol.TileCache and use it in ol.TileLayer

src/ol/TileCache.js

@@ -0,0 +1,29 @@
+goog.provide('ol.TileCache');
+
+goog.require('goog.structs.LinkedMap');
+
+/**
+ * A cache of ol.Tile objects.
+ * @constructor
+ * @extends {goog.structs.LinkedMap}
+ * @param {number=} opt_size
+ */
+ol.TileCache = function(opt_size) {
+    /**
+     * @constant
+     * @type {number}
+     */
+    this.size_ = opt_size || 100;
+
+    goog.base(this, 1, true /* cache mode */);
+};
+
+goog.inherits(ol.TileCache, goog.structs.LinkedMap);
+
+/**
+ * @inheritDoc
+ */
+ol.TileCache.prototype.removeNode = function(node) {
+    goog.base(this, 'removeNode', node);
+    node.value.destroy();
+};