JS: Format if statements with no else on a single line

test/codegen/expect/js/js.js

 dart_library.library('js/js', null, /* Imports */[
   "dart/_runtime",
   'dart/js',
   'dart/core'
 ], /* Lazy imports */[
 ], function(exports, dart, js, core) {
   'use strict';
   let dartx = dart.dartx;
   dart.export_(exports, js, ['allowInterop', 'allowInteropCaptureThis'], []);
   class JS extends core.Object {
     JS(name) {
-      if (name === void 0)
-        name = null;
+      if (name === void 0) name = null;
       this.name = name;
     }
   }
   dart.setSignature(JS, {
     constructors: () => ({JS: [JS, [], [core.String]]})
   });
   class _Anonymous extends core.Object {
     _Anonymous() {
     }
   }
   dart.setSignature(_Anonymous, {
     constructors: () => ({_Anonymous: [_Anonymous, []]})
   });
   const anonymous = dart.const(new _Anonymous());
   // Exports:
   exports.JS = JS;
   exports.anonymous = anonymous;
 });