Add ol.Map#getTargetElement

ol.Map#getTarget returns an element or a string, depending on what was passed to setTarget. This commit adds a getTargetElement method that always returns an Element.

src/ol/map.js

@@ -645,6 +645,19 @@ goog.exportProperty(
     ol.Map.prototype.getTarget);
 
 
+/**
+ * Get the DOM element into which this map is rendered. In contrast to
+ * `getTarget` this method always return an `Element`, or `null` if the
+ * map has no target.
+ * @return {Element} The element that the map is rendered in.
+ * @api
+ */
+ol.Map.prototype.getTargetElement = function() {
+  var target = this.getTarget();
+  return goog.isDef(target) ? goog.dom.getElement(target) : null;
+};
+
+
 /**
  * @param {ol.Pixel} pixel Pixel.
  * @return {ol.Coordinate} Coordinate.