Letting the map ask renderer for resolution.

src/ol/renderer/MapRenderer.js

@@ -58,6 +58,13 @@ ol.renderer.MapRenderer.prototype.getContainerSize = function() {
 ol.renderer.MapRenderer.prototype.draw = function(layers, center, resolution, animate) {
 };
 
+/**
+ * @return {number} The rendered resolution.
+ */
+ol.renderer.MapRenderer.prototype.getResolution = function() {
+    return this.renderedResolution_;
+};
+
 /**
  * TODO: determine a closure friendly way to register map renderers.
  * @type {Array}