Launcher performance optimizations: shaving about 3ms off Workspace.dispatchDraw()

    -> Caching values of getChildOffset() and getChildRelativeOffset()
    -> Using fast invalidate pattern in workspace#screenscrolled
    -> eliminated updateAdjacentPageAlpha, combined with screenScrolled
       code where appropriate to take advantage of fast invalidate
    -> removed a bit of dead code (just for cleanups sake)

Change-Id: Id91542ff846d9495a0370707d02d1f647dab22d4
3 files changed