First cut of mini dart:html.

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, SplayTreeSet;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/src/generated/ast.dart' hide ConstantEvaluator;
@@ skipping 1071 matching lines @@
       superCtor = element.supertype.element.unnamedConstructor;
       if (superCtor == null) {
         // This will only happen if the code has errors:
         // we're trying to generate an implicit constructor for a type where
         // we don't have a default constructor in the supertype.
         assert(options.forceCompile);
         return null;
       }
     }
 
+    if (superCtor == null) {
+      print('Error generating: ${element.displayName}');
+    }
     if (superCtor.name == '' && !_shouldCallUnnamedSuperCtor(element)) {
       return null;
     }
 
     var name = _constructorName(superCtor);
     var args = node != null ? _visit(node.argumentList) : [];
     return js.statement('super.#(#);', [name, args])..sourceInformation = node;
   }
 
   bool _shouldCallUnnamedSuperCtor(ClassElement e) {
@@ skipping 2419 matching lines @@
 
 /// A special kind of element created by the compiler, signifying a temporary
 /// variable. These objects use instance equality, and should be shared
 /// everywhere in the tree where they are treated as the same variable.
 class TemporaryVariableElement extends LocalVariableElementImpl {
   TemporaryVariableElement.forNode(Identifier name) : super.forNode(name);
 
   int get hashCode => identityHashCode(this);
   bool operator ==(Object other) => identical(this, other);
 }