Only test globals on ES6 browses.

test/unit/globals.html

@@ -52,6 +52,8 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
       listeners: {
         tap: 'handleTap'
       },
+      observeFooDeep() {},
+      observeFoo() {}
     });
   });
   </script>
@@ -63,6 +65,13 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 
 suite('globals', function() {
 
+  // Only run on native ES6 browsers, to avoid transpiler globals
+  try {
+    eval('class Foo {}');
+  } catch(e) {
+    this.skip();
+  }
+
   var expected = {
     origOwnProps: true,