fix #214, check type of inferred initializing formal with default value

lib/runtime/dart/async.js

 dart.library('dart/async', null, /* Imports */[
   'dart/core',
   'dart/_internal',
   'dart/collection'
 ], /* Lazy imports */[
   'dart/_isolate_helper',
   'dart/_js_helper'
 ], function(exports, core, _internal, collection, _isolate_helper, _js_helper) {
   'use strict';
   function _invokeErrorHandler(errorHandler, error, stackTrace) {
@@ skipping 5073 matching lines @@
       this.errorCallback = errorCallback;
       this.scheduleMicrotask = scheduleMicrotask;
       this.createTimer = createTimer;
       this.createPeriodicTimer = createPeriodicTimer;
       this.print = print;
       this.fork = fork;
     }
   }
   _ZoneSpecification[dart.implements] = () => [ZoneSpecification];
   dart.setSignature(_ZoneSpecification, {
-    constructors: () => ({_ZoneSpecification: [_ZoneSpecification, [], {handleUncaughtError: core.Object, run: core.Object, runUnary: core.Object, runBinary: core.Object, registerCallback: core.Object, registerUnaryCallback: core.Object, registerBinaryCallback: core.Object, errorCallback: core.Object, scheduleMicrotask: core.Object, createTimer: core.Object, createPeriodicTimer: core.Object, print: core.Object, fork: core.Object}]})
+    constructors: () => ({_ZoneSpecification: [_ZoneSpecification, [], {handleUncaughtError: HandleUncaughtErrorHandler, run: RunHandler, runUnary: RunUnaryHandler, runBinary: RunBinaryHandler, registerCallback: RegisterCallbackHandler, registerUnaryCallback: RegisterUnaryCallbackHandler, registerBinaryCallback: RegisterBinaryCallbackHandler, errorCallback: ErrorCallbackHandler, scheduleMicrotask: ScheduleMicrotaskHandler, createTimer: CreateTimerHandler, createPeriodicTimer: CreatePeriodicTimerHandler, print: PrintHandler, fork: ForkHandler}]})
   });
   class ZoneDelegate extends core.Object {}
   class Zone extends core.Object {
     _() {
     }
     static get current() {
       return Zone._current;
     }
     static _enter(zone) {
       dart.assert(zone != null);
@@ skipping 797 matching lines @@
   exports.ScheduleMicrotaskHandler = ScheduleMicrotaskHandler;
   exports.CreateTimerHandler = CreateTimerHandler;
   exports.CreatePeriodicTimerHandler = CreatePeriodicTimerHandler;
   exports.PrintHandler = PrintHandler;
   exports.ForkHandler = ForkHandler;
   exports.ZoneSpecification = ZoneSpecification;
   exports.ZoneDelegate = ZoneDelegate;
   exports.Zone = Zone;
   exports.runZoned = runZoned;
 });