base

Fix jank while unlocking and security is set

- Delay showing the bouncer and playing the entrance animation for a
  couple of frames.
- Do not disable back button on the normal Keyguard. This makes the
  entrance animation nicer and fixes some jank due to the need to
  draw into both windows.
- Prevent setPadding(...) call when nothing changes. setPadding would
  invalidate the padding for the whole view hierarchy, which results
  in a slower measure() when setting the window to invisible.

Bug: 17419960
Change-Id: I4a239d4af40ad86875e4a0dd08473f19a5c9b961