Support pixelRatio during reprojection

src/ol/source/tilesource.js

@@ -230,6 +230,14 @@ ol.source.Tile.prototype.getTileCacheForProjection = function(projection) {
 };
 
 
+/**
+ * @return {number}
+ */
+ol.source.Tile.prototype.getTilePixelRatio = function() {
+  return this.tilePixelRatio_;
+};
+
+
 /**
  * @param {number} z Z.
  * @param {number} pixelRatio Pixel ratio.