Use where function in MVT tests

test/spec/ol/format/mvtformat.test.js

@@ -1,7 +1,6 @@
 goog.provide('ol.test.format.MVT');
 
-(typeof ArrayBuffer == 'function' ? describe : xdescribe)('ol.format.MVT',
-    function() {
+where('ArrayBuffer').describe('ol.format.MVT', function() {
 
   var data;
   beforeEach(function(done) {

test/test-extensions.js

@@ -459,6 +459,7 @@
   };
 
   var features = {
+    ArrayBuffer: typeof ArrayBuffer === 'function',
     Uint8ClampedArray: ('Uint8ClampedArray' in global)
   };