Fix Recent Apps jumping artifact

When removing an item from the Recents list such that the list went from
larger than the screen to smaller (bringing the first item completely into view)
there was an artifact where the list would jump briefly, just prior to running
the transition to animate the remaining items into place.

The problem was that the custom ScrollView classes in the Recents app were
manipulating the scrollX/Y values of the items as a side-effect of any resize
of the list. Meanwhile, the LayoutTransition was manipulating both the size and
the scroll position of the list. The transition's scroll values would get clobbered by
the app's side-effect operation, causing the jump that we'd see on the screen.

The fix was to disable the side-effect operation during a layout transition.

Change-Id: I17f3f05d0e8a792e41bd46869ee700f128e63216