Introduces mouse actions for popup menu.

- mouse hover moves the selected item in the menu. It moves
  the selection rectangle, and further up/down key or enter
  key will start from the hovered item.
- when the mouse exits from the entire popup window, the
  selection is canceled. Further up/down key will start from
  the first item.

To implement these behaviors, and consider about other keyboard
behaviors which is special to menus, I believe it justifies
to create another class for the menu popups rather than using
ListPopupWindow directly.

Bug: 19642104
Change-Id: I5e405c0491c67fdef9764898701119979ec13a9f