fix super ctor logic

lib/src/codegen/js_codegen.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 dev_compiler.src.codegen.js_codegen;
 
 import 'dart:collection' show HashSet, HashMap;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/src/generated/ast.dart' hide ConstantEvaluator;
@@ skipping 633 matching lines @@
     return js.statement('dart.virtualField(#, #)', [
       cls.name,
       _emitMemberName(e.name, type: cls.type)
     ]);
   }
 
   /// Generates the implicit default constructor for class C of the form
   /// `C() : super() {}`.
   JS.Method _emitImplicitConstructor(
       ClassDeclaration node, String name, List<FieldDeclaration> fields) {
+    assert(_hasUnnamedConstructor(node.element) == fields.isNotEmpty);
+
     // If we don't have a method body, skip this.
     if (fields.isEmpty) return null;
 
     dynamic body = _initializeFields(fields);
     var superCall = _superConstructorCall(node);
     if (superCall != null) body = [[body, superCall]];
     return new JS.Method(
         _propertyName(name), js.call('function() { #; }', body));
   }
 
@@ skipping 104 matching lines @@
 
     var name = _constructorName(className, node.constructorName);
     return js.statement('this.#(#);', [name, _visit(node.argumentList)]);
   }
 
   JS.Statement _superConstructorCall(ClassDeclaration clazz,
       [SuperConstructorInvocation node]) {
     var superCtorName = node != null ? node.constructorName : null;
 
     var element = clazz.element;
-    if (superCtorName == null &&
-        (element.type.isObject || element.supertype.isObject)) {
+    if (superCtorName == null && !_shouldCallUnnamedSuperCtor(element)) {
       return null;
     }
 
     var supertypeName = element.supertype.name;
     var name = _constructorName(supertypeName, superCtorName);
 
     var args = node != null ? _visit(node.argumentList) : [];
     return js.statement('super.#(#);', [name, args])..sourceInformation = node;
   }
 
+  bool _shouldCallUnnamedSuperCtor(ClassElement e) {
+    var supertype = e.supertype;
+    if (supertype == null) return false;
+    if (_hasUnnamedConstructor(supertype.element)) return true;
+    for (var mixin in e.mixins) {
+      if (_hasUnnamedConstructor(mixin.element)) return true;
+    }
+    return false;
+  }
+
+  bool _hasUnnamedConstructor(ClassElement e) {
+    if (e.type.isObject) return false;
+    if (!e.unnamedConstructor.isSynthetic) return true;
+    return e.fields.any((f) => !f.isStatic && !f.isSynthetic);
+  }
+
   /// Initialize fields. They follow the sequence:
   ///
   ///   1. field declaration initializer if non-const,
   ///   2. field initializing parameters,
   ///   3. constructor field initializers,
   ///   4. initialize fields not covered in 1-3
   JS.Statement _initializeFields(List<FieldDeclaration> fieldDecls,
       [FormalParameterList parameters,
       NodeList<ConstructorInitializer> initializers]) {
 
@@ skipping 1569 matching lines @@
   return filepath;
 }
 
 // TODO(jmesserly): validate the library. See issue #135.
 bool _isJsNameAnnotation(DartObjectImpl value) => value.type.name == 'JsName';
 
 // TODO(jacobr): we would like to do something like the following
 // but we don't have summary support yet.
 // bool _supportJsExtensionMethod(AnnotatedNode node) =>
 //    _getAnnotation(node, "SupportJsExtensionMethod") != null;