Magnification bounds not always animated on a looper thread.

In display manigfication mode we are showing a frame around the
magnified region. Showing and hiding this frame is animated. In
some cases the code calling into the display magnifier is not
running on a looper thread which leads to a crash when interacting
with the property animator. Now the animation is explicitly handled
in a dedicated handler that runs on the window manager's handler
looper thread.

bug:15506701

Change-Id: I3fada775c9fac8820599dd31ac80720021c70cb3