message: fix the mser issue
diff: @@ -335,6 +335,8 @@ public:
  head = comp1->head;
  tail = comp2->tail;
  size = comp1->size + comp2->size;
  + // update the history size
  + history->size =size;
  CompHistory *h1 = history->child_;
  CompHistory *h2 = comp2->history;
  