Notify IME visibility when showWindow is called.

To change the back icon, need to notify IME visibility to the
InputMethodManagerService when guest IME service calls showWindow().

IME can call showWindow() if it want to show software input, but it
doesn't send IME_VISIBLE state to the InputMethodManagerService,
hence the arrow icon is different from what we expect. This
typically happens when Latin IME shows Emoji panel by left-alt keys.

Bug: 20318050

Change-Id: I0ec2c71ad9bc3b7e9259d9180375d9062fc7e154