Fix tapping on divider bar several times makes split sloggish

Make sure it won't introduce redundant fling animation when touch on
divider bar didn't exceed tap threshold. This make sure it won't queue
extra sync transactions with SyncTransactionQueue. Also skip redundant
checks after detected double tap in staged split.

Fix: 186626153
Fix: 179004532
Test: tapping on divider bar of legacy and staged split, it won't make
split sloggish.

Change-Id: I2a326f54f25d77e86fa51bca67b68daca21dedfc