Add ElementKind for factory constructors.

pkg/compiler/lib/src/elements/common.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.
 
 /// Mixins that implement convenience methods on [Element] subclasses.
 
 library elements.common;
 
 import '../common/names.dart' show
     Names,
@@ skipping 42 matching lines @@
   bool get isConstructor => isGenerativeConstructor ||  isFactoryConstructor;
 
   @override
   bool get isGenerativeConstructor =>
       kind == ElementKind.GENERATIVE_CONSTRUCTOR;
 
   @override
   bool get isGenerativeConstructorBody =>
       kind == ElementKind.GENERATIVE_CONSTRUCTOR_BODY;
 
+  bool get isFactoryConstructor =>
+      kind == ElementKind.FACTORY_CONSTRUCTOR;
+
   @override
   bool get isVariable => kind == ElementKind.VARIABLE;
 
   @override
   bool get isField => kind == ElementKind.FIELD;
 
   @override
   bool get isAbstractField => kind == ElementKind.ABSTRACT_FIELD;
 
   @override
@@ skipping 411 matching lines @@
       // this signature must not have more required parameters.  Having more
       // optional parameters is not a problem, they simply are never provided
       // by call sites of a call to a method with the other signature.
       int otherTotalCount = signature.parameterCount;
       return requiredParameterCount <= otherTotalCount
           && parameterCount >= otherTotalCount;
     }
     return true;
   }
 }