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

src/ol/layer/TileLayer.js

@@ -1,6 +1,7 @@
 goog.provide('ol.layer.TileLayer');
 
 goog.require('ol.layer.Layer');
+goog.require('ol.TileCache');
 
 /**
  * @constructor
@@ -68,6 +69,12 @@ ol.layer.TileLayer = function() {
      */
     this.resolutions_ = null;
 
+    /**
+     * @private
+     * @type {ol.TileCache}
+     */
+    this.cache_ = new ol.TileCache();
+
 };
 
 goog.inherits(ol.layer.TileLayer, ol.layer.Layer);
@@ -214,3 +221,18 @@ ol.layer.TileLayer.prototype.setNumZoomLevels = function(numZoomLevels) {
 ol.layer.TileLayer.prototype.setResolutions = function(resolutions) {
     this.resolutions_ = resolutions;
 };
+
+/**
+ * Get a tile from the cache, or create a tile and add to
+ * the cache.
+ * @param url {string}
+ * @param bounds {ol.Bounds}
+ */
+ol.layer.TileLayer.prototype.getTile = function(url, bounds) {
+    var tile = this.cache_.get(url);
+    if (!goog.isDef(tile)) {
+        tile = new ol.Tile(url, bounds);
+        this.cache_.set(tile.getUrl(), tile);
+    }
+    return tile;
+};

src/ol/layer/XYZ.js

@@ -25,6 +25,17 @@ ol.layer.XYZ = function(url) {
     goog.base(this);
 
     this.setMaxResolution(156543.03390625);
+
+    this.setResolutions([
+        156543.03390625, 78271.516953125, 39135.7584765625,
+        19567.87923828125, 9783.939619140625, 4891.9698095703125,
+        2445.9849047851562, 1222.9924523925781, 611.4962261962891,
+        305.74811309814453, 152.87405654907226, 76.43702827453613,
+        38.218514137268066, 19.109257068634033, 9.554628534317017,
+        4.777314267158508, 2.388657133579254, 1.194328566789627,
+        0.5971642833948135, 0.29858214169740677, 0.14929107084870338,
+        0.07464553542435169
+    ]);
 };
 
 goog.inherits(ol.layer.XYZ, ol.layer.TileLayer);
@@ -81,7 +92,7 @@ ol.layer.XYZ.prototype.getData = function(bounds, resolution) {
             url = me.url_.replace('{x}', offsetX + x + '')
                          .replace('{y}', offsetY + y + '')
                          .replace('{z}', zoom + '');
-            tile = new ol.Tile(url, tileBounds);
+            tile = this.getTile(url, tileBounds);
             tiles[y][x] = tile;
         }
     }