Revert "Drop trailing null arguments in generated JS."

tests/compiler/dart2js/drop_trailing_null_arguments_test.dart

-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-// Test that parameters keep their names in the output.
-
-import 'package:async_helper/async_helper.dart';
-import 'package:expect/expect.dart';
-import 'compiler_helper.dart';
-
-main() {
-  // If a function call has trailing 'null' arguments, we can safely skip
-  // them as JavaScript will fill missing arguments with 'undefined'.
-  asyncTest(() => compile(r"""
-      class It<A, B> {
-        It([a, b, c]) : super;
-      }
-
-      foo(a,b,c) => a;
-      test() {
-        foo(1, null, null);
-        foo(2, 3, null);
-        new It();
-        new It(null, 1);
-      }
-      """,
-      entry: 'test', minify: false).then((String generated) {
-    Expect.isTrue(generated.contains(r"foo(1)"));
-    Expect.isTrue(generated.contains(r"foo(2, 3)"));
-    Expect.isTrue(generated.contains(r"It$()"));
-    Expect.isTrue(generated.contains(r"It$(null, 1)"));
-  }));
-}