Add new container which don't stop event propagation

and allow overlays to optionnally stop event propagation

src/ol/overlay.js

@@ -60,6 +60,12 @@ ol.Overlay = function(options) {
 
   goog.base(this);
 
+  /**
+   * @private
+   * @type {boolean}
+   */
+  this.stopEvent_ = goog.isDef(options.stopEvent) ? options.stopEvent : false;
+
   /**
    * @private
    * @type {Element}
@@ -202,8 +208,10 @@ ol.Overlay.prototype.handleMapChanged = function() {
     this.mapPostrenderListenerKey_ = goog.events.listen(map,
         ol.MapEventType.POSTRENDER, this.handleMapPostrender, false, this);
     this.updatePixelPosition_();
-    goog.dom.append(
-        /** @type {!Node} */ (map.getOverlayContainer()), this.element_);
+    goog.dom.append(/** @type {!Node} */ (
+        this.stopEvent_ ? map.getOverlayContainerStopEvent() :
+                          map.getOverlayContainer()),
+        this.element_);
   }
 };