Support ClassMirror.newInstance on factory constructors

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 421 matching lines @@
     if (typeArgs == null) {
       _typeArguments = const [];
     } else {
       _typeArguments =
           new List.unmodifiable(typeArgs.map((t) => reflectType(_wrap(t))));
     }
   }
 
   InstanceMirror newInstance(Symbol constructorName, List args,
       [Map<Symbol, dynamic> namedArgs]) {
-    // TODO(vsm): Support factory constructors and named arguments.
+    // TODO(vsm): Support named arguments.
     var name = getName(constructorName);
     assert(namedArgs == null || namedArgs.isEmpty);
+    // Default constructors are mapped to new.
     if (name == '') name = 'new';
-    var instance = JS('', 'new (#.#)(...#)', _unwrap(_cls), name, args);
+    var cls = _unwrap(_cls);
+    var ctr = JS('', '#.#', cls, name);
+    // Only generative Dart constructors are wired up as real JS constructors.
+    var instance = JS('bool', '#.prototype == #.prototype', cls, ctr)
+        // Generative
+        ? JS('', 'new #(...#)', ctr, args)
+        // Factory
+        : JS('', '#(...#)', ctr, args);
     return reflect(instance);
   }
 
   // TODO(vsm): Need to check for NSM, types on accessors below.  Unlike the
   // InstanceMirror case, there is no dynamic helper to delegate to - we never
   // need a dload, etc. on a static.
 
   InstanceMirror getField(Symbol symbol) {
     var name = getName(symbol);
     return reflect(JS('', '#[#]', _unwrap(_cls), name));
@@ skipping 201 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'";
 }