Merge pull request #7172 from f7o/ol-source-vectortile-clear

added clear method to vectortile source

src/ol/source/vectortile.js

@@ -96,6 +96,14 @@ ol.source.VectorTile.prototype.getOverlaps = function() {
   return this.overlaps_;
 };
 
+/**
+ * clear {@link ol.TileCache} and delete all source tiles
+ * @api
+ */
+ol.source.VectorTile.prototype.clear = function() {
+  this.tileCache.clear();
+  this.sourceTiles_ = {};
+};
 
 /**
  * @inheritDoc