Improve AnchoredWindow with smart positioning logic.

* Add appToken.
* Add mWindowSizeListenerView for getting the displayable window size
  (screen - system windows - soft input).
* Add mContentView when we have all the necesssary info.
* Change mContentView only if something changes (height, bounds,
  displayBounds).

Bug: 34637800
Test: CTS
Change-Id: Iade6179f6303a6d4777e99fa6c600ba6352ee863