Rely on IMM#focusOut() to close input session.

Historically we have been doing nothing in IMM#focusOut().
Problem of ignoring IMM#focusOut() may not be obvious as
long as IMM#focusIn() is called immediately after
IMM#focusOut().  In some particular situations, however,
IMM can fall into an inconsistent state where the software
keyboard continues to be shown even when there is no text
input field.

As reported in b.android.com/171190 or Bug 20820914, we
can easily reproduce that inconsistent state by removing
a focused EditText from the parent view while the IME still
keeps an active connection to the EditText.

This CL tries to address such a situation by staring using
IMM#focusOut() as another trigger to check IME focus.

Note that this CL has no effect if IMM#focusOut was called
after the current window losed the focus. It is supposed to
be taken care of in subsequent CLs for Bug 20612313.

This CL depends on Id6afc8fc64512225578c62557b96c7dc2e969adf.

Bug: 20612313
Change-Id: Ib1b037594ebbb4ad4cf2d59e21c7a8ca9d8dc930