Merge changes I8ac518ce,I8392b4c3,I3bef3f75

* changes:
  Support for activity to opt-in/out of PiP form of multi-window.
  API for moving top activity in a stack to pinned stack.
  Added support for pinned stack.
tree: 21b414bce18ed392dc21b6b5a8245da87c3137f2
  1. res/
  2. src/
  3. testing/
  4. tests/
  5. Android.mk
  6. AndroidManifest.xml
  7. wrap_alpha.py