Remove sequential_promise_test helper, just use promise_test

LayoutTests/resources/testharness-helpers.js

 /*
  * testharness-helpers contains various useful extensions to testharness.js to
  * allow them to be used across multiple tests before they have been
  * upstreamed. This file is intended to be usable from both document and worker
  * environments, so code should for example not rely on the DOM.
  */
 
 // Returns a promise that fulfills after the provided |promise| is fulfilled.
 // The |test| succeeds only if |promise| rejects with an exception matching
 // |code|. Accepted values for |code| follow those accepted for assert_throws().
@@ skipping 143 matching lines @@
         if (typeof src != "object")
             return src;
         var dst = Array.isArray(src) ? [] : {};
         for (var property in src) {
             dst[property] = deepCopy(src[property]);
         }
         return dst;
     }
     return JSON.stringify(deepCopy(object));
 }
-
-(function() {
-  var promise_tests = Promise.resolve();
-  // Helper function to run promise tests one after the other.
-  // TODO(ortuno): Remove once https://github.com/w3c/testharness.js/pull/115/files
-  // gets through.
-  function sequential_promise_test(func, name) {
-    var test = async_test(name);
-    promise_tests = promise_tests.then(function() {
-      return test.step(func, test, test);
-    }).then(function() {
-      test.done();
-    }).catch(test.step_func(function(value) {
-      // step_func catches the error again so the error doesn't propagate.
-      throw value;
-    }));
-  }
-
-  self.sequential_promise_test = sequential_promise_test;
-})();