code: private boolean isTypedTimeLegalSoFar() {
          Node node = mLegalTimesTree;
          for (int keyCode : mTypedTimes) {
              node = node.canReach(keyCode);
              if (node == null) {
                  return false;
              }
          }
          return true;
      }
docs: Traverse the tree to see if the keys that have been typed so far are legal as is,
  or may become legal as more keys are typed (excluding backspace).