Fix floating toolbar flickers.

-Flicker was a side effect the delay in hiding the toolbar when
there is a down press on a TextView handle. The timing clashed
with the time it takes for the FloatingActionMode to release a
hide lock on a changing content rect. Extra flickers also happened
if the ActionMode happened to be invalidated at about the same time.
Since there was no longer a hide lock, the toolbar refreshed, getting
rid of the "Select all" menu item.
FIX. I believe we don't need the delayed hide on down press on a
TextView handle. I've removed this.

-I've also updated FloatingActionMode to ensure that hide locks
overlap one another if necessary. The toolbar can only be visible if
all locks are off.

Bug: 21793687
Change-Id: I290ea45ab17d5862b453cb319afb4c8ffe084cd0