Set preload appropriately in examples

examples/animation.js

@@ -23,6 +23,7 @@ var bern = ol.projection.transform(
 var map = new ol.Map({
   layers: [
     new ol.layer.TileLayer({
+      preload: true,
       source: new ol.source.OpenStreetMap()
     })
   ],

examples/bing-maps.js

@@ -12,6 +12,7 @@ var layers = [];
 for (var i = 0; i < styles.length; ++i) {
   layers.push(new ol.layer.TileLayer({
     visible: false,
+    preload: true,
     source: new ol.source.BingMaps({
       key: 'AgtFlPYDnymLEe9zJ5PCkghbNiFZE9aAtTy3mPaEnEBXqLHtFuTcKoZ-miMC3w7R',
       style: styles[i]

examples/rotation.js

@@ -9,6 +9,7 @@ goog.require('ol.source.OpenStreetMap');
 var map = new ol.Map({
   layers: [
     new ol.layer.TileLayer({
+      preload: true,
       source: new ol.source.OpenStreetMap()
     })
   ],

examples/stamen.js

@@ -10,6 +10,7 @@ goog.require('ol.source.Stamen');
 var map = new ol.Map({
   layers: [
     new ol.layer.TileLayer({
+      preload: true,
       source: new ol.source.Stamen({
         layer: 'watercolor'
       })