Return a promise from Env#execute in environments that support promises

[#178373231]

spec/helpers/promises.js

@@ -4,4 +4,10 @@
       env.pending('Environment does not support promises');
     }
   };
+
+  env.requireNoPromises = function() {
+    if (typeof Promise === 'function') {
+      env.pending('Environment supports promises');
+    }
+  };
 })(jasmine.getEnv());