Actually enforce having space between the close button and infobar content.
(Previously, we omitted the desired space when calculating the infobar layout as
the user shrunk the infobar narrower.)

Make this spacing match the end-of-label spacing, because there's no obvious
reason for it to be a random different value.

Return a minimum width for infobars so that, now that the frame layout code is
paying attention to them, the browser min width will actually respect the
infobar min width.

There are still a lot of problems with the individual infobars' actual min width
calculations, those will be fixed in a future patch.

BUG=none
TEST=Show an infobar and shrink the window width, it should be harder to get the infobar contents to all overlap each other
R=msw@chromium.org

Review URL: https://codereview.chromium.org/108183005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239861 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239861