anchor.diff:        Node node, TreeElements definitions,
         {bool isConst: true}) {
       assert(node != null);
  -    CompileTimeConstantEvaluator evaluator = new CompileTimeConstantEvaluator(
  -        this, definitions, compiler,
  -        isConst: isConst);
  -    AstConstant constant = evaluator.evaluate(node);
  -    if (constant != null) {
  -      cacheConstantValue(constant.expression, constant.value);
  -      return constant.expression;
  -    }
       return null;
     }
   
  
positive.code: 
  library dart2js.compile_time_constant_evaluator;
  
  import 'common/resolution.dart' show Resolution;
  import 'common/tasks.dart' show CompilerTask, Measurer;
  import 'common.dart';
  import 'compiler.dart' show Compiler;
  import 'constant_system_dart.dart';
  import 'constants/constant_system.dart';
  import 'constants/constructors.dart';
  import 'constants/evaluation.dart';
  import 'constants/expressions.dart';
  import 'constants/values.dart';
  import 'common_elements.dart' show CommonElements;
  import 'elements/elements.dart';
  import 'elements/types.dart' show DartTypes;
  import 'elements/modelx.dart' show ConstantVariableMixin;
  import 'elements/operators.dart';
  import 'elements/resolution_types.dart';
  import 'resolution/tree_elements.dart' show TreeElements;
  import 'resolution/deferred_load.dart' show AstDeferredLoadTask;
  import 'tree/tree.dart';
  import 'universe/call_structure.dart' show CallStructure;
  import 'util/util.dart' show Link;
  
  /// A [ConstantEnvironment] provides access for constants compiled for variable
  /// initializers.
  
negative.code:   }
  
    @override
    void evaluate(ConstantExpression constant) {}
  
    ConstantExpression compileVariable(VariableElement element) {
      return internalCompileVariable(element, false, true);
  