Use interim tiles when changing dynamic parameters

src/ol/tile.js

@@ -44,6 +44,22 @@ ol.Tile = function(tileCoord, state) {
    */
   this.state = state;
 
+  /**
+   * An "interim" tile for this tile. The interim tile may be used while this
+   * one is loading, for "smooth" transitions when changing params/dimensions
+   * on the source.
+   * @type {ol.Tile}
+   */
+  this.interimTile = null;
+
+  /**
+   * A key assigned to the tile. This is used by the tile source to determine
+   * if this tile can effectively be used, or if a new tile should be created
+   * and this one be used as an interim tile for this new tile.
+   * @type {string}
+   */
+  this.key = '';
+
 };
 goog.inherits(ol.Tile, goog.events.EventTarget);