Tighten up handling of JS types and add test.

pkg/dev_compiler/tool/input_sdk/private/js_mirrors.dart

 // Copyright (c) 2015, 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.
 
 library dart._js_mirrors;
 
 import 'dart:mirrors';
 import 'dart:_foreign_helper' show JS;
 import 'dart:_internal' as _internal;
 
@@ skipping 31 matching lines @@
     return JS('', '#.value', property);
   }
   // TODO(vsm): Might not be a class.
   var mirror = new JsClassMirror._(key);
   JS('', '#[#] = #', unwrapped, _typeMirror, mirror);
   return mirror;
 }
 
 final dynamic _dart = JS('', 'dart');
 
-dynamic _dload(obj, String name) {
+dynamic _dload(obj, name) {
   return JS('', '#.dloadMirror(#, #)', _dart, obj, name);
 }
 
-void _dput(obj, String name, val) {
+void _dput(obj, name, val) {
   JS('', '#.dputMirror(#, #, #)', _dart, obj, name, val);
 }
 
 dynamic _dcall(obj, List args) {
   return JS('', '#.dcall(#, ...#)', _dart, obj, args);
 }
 
-dynamic _dsend(obj, String name, List args) {
+dynamic _dsend(obj, name, List args) {
   return JS('', '#.dsend(#, #, ...#)', _dart, obj, name, args);
 }
 
 dynamic _getGenericClass(obj) {
   return JS('', '#.getGenericClass(#)', _dart, obj);
 }
 
 dynamic _getGenericArgs(obj) {
   return JS('', '#.getGenericArgs(#)', _dart, obj);
 }
@@ skipping 579 matching lines @@
       var param =
           new JsParameterMirror._(new Symbol(''), _wrap(type), metadata);
       params[i + args.length] = param;
     }
 
     _params = new List.unmodifiable(params);
   }
 
   String toString() => "MethodMirror on '$_name'";
 }