anchor.diff:  
     @override
     void visitVariableDeclaration(ir.VariableDeclaration node) {
  -    registerSeenClasses(node.type);
       if (node.initializer != null) {
         visitNode(node.initializer);
       } else {
  
positive.code:   void visitIsExpression(ir.IsExpression node) {
      impactBuilder.registerTypeUse(
          new TypeUse.isCheck(elementMap.getDartType(node.type)));
      registerSeenClasses(node.type);
      visitNode(node.operand);
    }
  
  
negative.code:   void visitStaticSet(ir.StaticSet node) {
      visitNode(node.value);
      MemberEntity member = elementMap.getMember(node.target);
      impactBuilder.registerStaticUse(new StaticUse.staticSet(member));
    }
  
  