fix mixins with factory constructors

pkg/dev_compiler/lib/src/compiler/code_generator.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.
 
 import 'dart:collection' show HashMap, HashSet;
 import 'dart:math' show min, max;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1757 matching lines @@
     if (ctors.isEmpty) {
       var superCall = _superConstructorCall(classElem, className);
       List<JS.Statement> body = [_initializeFields(fields)];
       if (superCall != null) body.add(superCall);
 
       addConstructor(classElem.unnamedConstructor,
           _finishConstructorFunction([], new JS.Block(body), isCallable));
       return;
     }
 
+    bool foundConstructor = false;
     for (var ctor in ctors) {
       var element = ctor.element;
       if (element.isFactory || _externalOrNative(ctor)) continue;
 
       addConstructor(
           element, _emitConstructor(ctor, fields, isCallable, className));
+      foundConstructor = true;
+    }
+
+    // If classElement has only factory constructors, and it can be mixed in,
+    // then we need to emit a special hidden default constructor for use by
+    // mixins.
+    if (!foundConstructor && classElem.supertype.isObject) {
+      body.add(
+          js.statement('(#[#] = function() { # }).prototype = #.prototype;', [
+        className,
+        _callHelper('mixinNew'),
+        [_initializeFields(fields)],
+        className
+      ]));
     }
   }
 
   /// Emits static fields for a class, and initialize them eagerly if possible,
   /// otherwise define them as lazy properties.
   void _emitStaticFields(List<FieldDeclaration> staticFields,
       ClassElement classElem, List<JS.Statement> body) {
     var lazyStatics = staticFields.expand((f) => f.fields.variables).toList();
     if (lazyStatics.isNotEmpty) {
       body.add(_emitLazyFields(classElem, lazyStatics));
@@ skipping 4117 matching lines @@
   if (targetIdentifier.staticElement is! PrefixElement) return false;
   var prefix = targetIdentifier.staticElement as PrefixElement;
 
   // The library the prefix is referring to must come from a deferred import.
   var containingLibrary = resolutionMap
       .elementDeclaredByCompilationUnit(target.root as CompilationUnit)
       .library;
   var imports = containingLibrary.getImportsWithPrefix(prefix);
   return imports.length == 1 && imports[0].isDeferred;
 }