Floating Toolbar: Wrap the ActionBar ActionMode handling.

Refactor the ActionBar handling of startActionMode to allow handling by
the ActionModeWrapper, using the previously created infrastructure.

Things pending after this CL:
- Representing the floating type
- Supporting two ActionModes in parallel in DecorView, one of each type

Change-Id: Ic126e004bdef5d91d8be3d6a07eea34aa97a611e