Change the multi-tap recognition logic of TapGesture.

Change the multi-tap recognition logic of TapGesture.
Previously, we checked how many TouchDowns occurred within mMaximumAllowedTime.

Now, after a tap occurs, if the next touchdown occurs within mMaximumAllowedTime., it is recognized as a multi-tap.

ex) If it's a double tap, it's like this:
|(touch down <--recognizerTime--> touch up) <--  wihtin maximumAllowedTime --> (touch down <--recognizerTime--> touch up)|

Change-Id: I8b33bfbe09729d558bb8495738259ae5a757ddc9