Store mHistoricTimes as longs intead of floats

The loss of precision was causing us to miscalculate the age of
events, and thus not detecting any pause due to denominator = 0.

Test: have a device that hasn't been rebooted for a certain
amount of time such that SystemClock#uptimeMillis can't be
accurately converted to a float, then try to swipe up and hold

Fixes: 160568387
Change-Id: Idef112187f34a18feea7e6a0b77258626f9d0ed4