The current use of the SCROLL_PREFILING hint hurts scroll performance
and results in a lot of dropped frames.
The hint ID corresponding to SCROLL_PREFILING only takes into effect for
a default timeout value of 80 ms (as found in perfboostsconfig.xml),
while the duration value in the process_interaction_hint function runs
for a much longer time, from 1500 ms up to 5000 ms (bounds of
kMinFlingDuration and kMaxInteractiveDuration). During the period
of time, when the timeout value has elapsed and current time is less
than duration, another interaction hint cannot be processed. Therefore,
if the user decides to scroll during this period, high frame drops can be
experienced as the CPU freq isn't raised by processing another hint to
account for this additional scrolling.
By only using SCROLL_VERTICAL, fluidity can be maintained, improving user
experience.
Change-Id: I2fbde8b2db6710d262e9a058e0bc9c02e524648c
5a704c4ac3