[Mac] Remove guard on FocusLocation() in autocomplete field.

[Mac] Remove guard on FocusLocation() in autocomplete field.

Reapplies http://codereview.chromium.org/149492 .  That version was
accidentally calling this code as part of the class implementation,
which caused the code to receive the "done editing" notification,
which caused the code to drop the popup...

This version stops using FocusLocation() internally, instead messaging
field_ directly.

http://crbug.com/12246
TEST=Type some stuff in address bar.  Popup should popup with suggestions.  With cursor still in bar, Command-l should select all.

[Scott Hess - ex-Googler, 2009-07-14 22:16:51]

I think the other change I proposed would have worked, but this one I'm pretty
confident in.  Making externally-exposed API work for internal use seemed like
such a good idea at the time, but the diverging needs always seem to trip me up,
so not so good in retrospect.

[Avi (use Gerrit), 2009-07-15 14:20:27]

LG