anchor.diff:  
     HBasicBlock dominator = null;
     final List<HBasicBlock> dominatedBlocks;
  +  int dominatorDfsIn;
  +  int dominatorDfsOut;
   
     HBasicBlock() : this.withId(null);
     HBasicBlock.withId(this.id)
  
positive.code:           block.assignCommonDominator(predecessors[j]);
          }
        }
      }
    }
  
  
negative.code:     return validator.isValid;
    }
  
    bool dominates(HBasicBlock other) {
      return this.dominatorDfsIn <= other.dominatorDfsIn &&
          other.dominatorDfsOut <= this.dominatorDfsOut;
    }
  
    toString() => 'HBasicBlock($id)';
  