Dispose of vector tiles properly

src/ol/vectortile.js

@@ -66,6 +66,18 @@ ol.VectorTile = function(tileCoord, state, src, format, tileLoadFunction) {
 ol.inherits(ol.VectorTile, ol.Tile);
 
 
+/**
+ * @inheritDoc
+ */
+ol.VectorTile.prototype.disposeInternal = function() {
+  this.features_ = null;
+  this.replayGroups_ = {};
+  this.state = ol.TileState.ABORT;
+  this.changed();
+  ol.Tile.prototype.disposeInternal.call(this);
+};
+
+
 /**
  * Get the feature format assigned for reading this tile's features.
  * @return {ol.format.Feature} Feature format.