Use a standard title attribute for the control buttons

src/ol/control/zoomtoextentcontrol.js

@@ -35,14 +35,10 @@ ol.control.ZoomToExtent = function(opt_options) {
 
   var tipLabel = goog.isDef(options.tipLabel) ?
       options.tipLabel : 'Fit to extent';
-  var tip = goog.dom.createDom(goog.dom.TagName.SPAN, {
-    'role' : 'tooltip'
-  }, tipLabel);
   var button = goog.dom.createDom(goog.dom.TagName.BUTTON, {
-    'class': 'ol-has-tooltip',
-    'type': 'button'
+    'type': 'button',
+    'title': tipLabel
   });
-  goog.dom.appendChild(button, tip);
 
   var buttonHandler = new ol.pointer.PointerEventHandler(button);
   this.registerDisposable(buttonHandler);