anchor.diff:    dump() {
       int interestingTypes = 0;
       int giveUpTypes = 0;
  -    returnTypeOf.forEach((Element method, TypeMask type) {
  +    returnTypeOf.forEach((Element element, TypeMask type) {
         if (isGiveUpType(type)) {
           giveUpTypes++;
         } else if (type != nullType && !isDynamicType(type)) {
           interestingTypes++;
         }
       });
  -    typeOf.forEach((Element method, TypeMask type) {
  +    typeOf.forEach((Element element, TypeMask type) {
         if (isGiveUpType(type)) {
           giveUpTypes++;
         } else if (type != nullType && !isDynamicType(type)) {
  
positive.code:           }
          }
          if (returnType == null) {
            returnType = new TypeMask.nonNullExact(
                mappedType.computeType(compiler));
          } else {
            return inferrer.dynamicType;
          }
  
negative.code:         compiler.intClass.rawType);
      doubleType = new TypeMask.nonNullExact(
          compiler.doubleClass.rawType);
      // TODO(ngeoffray): Switch to subtype once we do proper union.
      numType = new TypeMask.nonNullExact(
          compiler.numClass.rawType);
      stringType = new TypeMask.nonNullExact(
          compiler.stringClass.rawType);
  