Fix FloatingToolbar flickers.

This is fixed by avoiding calling toolbar.show() in PhoneWindow.
FloatingActionMode coordinates whether or not the toolbar should be
visible. PhoneWindow differs to it.

This CL also adds a new API:
ActionMode#onWindowFocusChanged(boolean)

Bug: 21617792
Change-Id: Ic49ce1000ce9c782d0f9e17e3d024d462c7b758b
5 files changed