Navigation control with Drag sequence Dragger

This is totally unfinished, but tests pass, and it is only meant to give the map a Navigation control.

src/ol/control/Navigation.js

@@ -5,7 +5,7 @@ goog.require('ol.control.Control');
 
 /**
  * @constructor
- * @extends ol.control.Control
+ * @extends {ol.control.Control}
  * @param {boolean|undefined} opt_autoActivate
  */
 ol.control.Navigation = function(opt_autoActivate) {
@@ -19,6 +19,18 @@ ol.control.Navigation = function(opt_autoActivate) {
      */
     this.autoActivate_ =
         goog.isDef(opt_autoActivate) ? opt_autoActivate : true;
+    
+    /**
+     * type {number}
+     * @private
+     */
+    this.oldX = undefined;
+
+    /**
+     * type {number}
+     * @private
+     */
+    this.oldY = undefined;
 
 };
 goog.inherits(ol.control.Navigation, ol.control.Control);
@@ -45,5 +57,7 @@ ol.control.Navigation.prototype.deactivate = function() {
  * @param {Event} evt
  */
 ol.control.Navigation.prototype.moveMap = function(evt) {
-    this.getMap().moveByPx(evt.dx, evt.xy);
+    this.getMap().moveByPx(evt.clientX - oldX, evt.clientY - oldY);
+    oldX = evt.clientX;
+    oldY = evt.clientY;
 };