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)

    Credits: Pawit Pornkitprasan

Change-Id: Iad52a35120212c871ffd35df6184aeb678ee44aa
framework:Thread synchronization for UI update

Issue : Framework reboot was observed due to out of sync between
        two threads which inturn causes Null pointer exception
        while updating airplanemode.
Fix : Handled Null pointer exception and the crash is not observed.
CRs-Fixed: 570122

Change-Id: I2e969f6e7726ffcf8648b366ebb54cb2b0afc292