Add rendering test for heatmap layer

rendering/cases/heatmap-layer/main.js

@@ -0,0 +1,44 @@
+import Map from '../../../src/ol/Map.js';
+import View from '../../../src/ol/View.js';
+import TileLayer from '../../../src/ol/layer/Tile.js';
+import XYZ from '../../../src/ol/source/XYZ';
+import {Heatmap as HeatmapLayer} from '../../../src/ol/layer';
+import VectorSource from '../../../src/ol/source/Vector';
+import KML from '../../../src/ol/format/KML';
+
+const vector = new HeatmapLayer({
+  source: new VectorSource({
+    url: '/data/2012_Earthquakes_Mag5.kml',
+    format: new KML({
+      extractStyles: false
+    })
+  }),
+  blur: 3,
+  radius: 3
+});
+
+vector.getSource().on('addfeature', function(event) {
+  const name = event.feature.get('name');
+  const magnitude = parseFloat(name.substr(2));
+  event.feature.set('weight', magnitude - 5);
+});
+
+const raster = new TileLayer({
+  source: new XYZ({
+    url: '/data/tiles/satellite/{z}/{x}/{y}.jpg',
+    transition: 0
+  })
+});
+
+new Map({
+  layers: [raster, vector],
+  target: 'map',
+  view: new View({
+    center: [0, 0],
+    zoom: 0
+  })
+});
+
+render({
+  message: 'Heatmap layer renders properly using webgl'
+});

rendering/data/2012_Earthquakes_Mag5.kml

@@ -0,0 +1 @@
+../../examples/data/kml/2012_Earthquakes_Mag5.kml