Fix restoring network mode preference on reboot.

When a user sets the option to use only 2G networks (for GSM networks) or its
equivalent for CDMA networks, each reboot erases that setting. That forces
the user to re-select the same option after each boot.
This (very simple) patch fixes it.

Change-Id: Ib9e4bba6da705c127ce1f3aa3c242b9262541cee
Improve scrolling cache

Scrolling cache helps make short scrolls/flings smooth but will
cause stutter when long flings are made. This patch disables
scrolling cache when long flings are made.

This patch also fixes a related bug where scrolling cache will
not be enabled properly when transitioning from flinging to scrolling.

Patch Set 2: Calculate threshold based on maximum velocity (Sang Tae Park)

Change-Id: I1fdbaad92263c9f983a32900e74eba1f0367902b