Hide leash at beginning of animation instead of alpha

As of now setting alpha zero is not interchangeable with hiding a
surface. Till that happens, we will explicity hide() to prevent any
visibility inconsistencies.

Fix: 141643119
Bug: 111084606
Test: Manually:
     1. Launch an that requests showSoftInput again onResume()
        e.g. Chrome
     2. Focus on Editor and then tap home (or swipe to home)
     3. relaunch app from recents or launcher
     4. IME should be visbile onResume().

Change-Id: I79877406ef24d1633a075fa5f7ef4141f3172678