Fix floating bookmark bar on windows.
Fix floating bookmark bar on windows.

IsBookmarkBarVisible() continues to have a consistent meaning across
platforms, but extra logic has been added to windows to be smarter
about when to show the bar.  Such extra logic also is consistent
across platforms (e.g. see browser_window_gtk.cc and
bookmark_bar_gtk.cc).

Problem introduced with http://codereview.chromium.org/1461001
BUG=http://crbug.com/39559

Review URL: http://codereview.chromium.org/1594009

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@43419 0039d316-1c4b-4281-b951-d872f2087c98

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