Fix bugs MultiShrinkScroller#snapToBottom()

* use distinct logic for deciding when to snapToBottom in landscape
* I was using the wrong constant in a calculation before. I was
  using mTransparentStartHeight instead of mIntermediateHeaderHeight.
  The result is subtle so I didn't notice until I looked at the code
  again.

Bug: 16875627
Change-Id: I6ede58afa3717540f01d8d59eaad80e11db7ac14