[Mac] Adjust toolbar spacing of browser actions for M6.

Toolbar.xib change brings browser-action container view out from under
Omnibox.

Push browser-action sizing code into controller to reduce exposed
constants.  Make size consistent with other toolbar buttons.  4px
visual spacing from omnibox to first browser action (grippy in that
area), between browser actions, and last action to wrench menu.

browser_actions_overflow_Template.pdf resource for browser-action
chevron.  Chevron same height as browser actions.  Get rid of divider
between browser actions and wrench (future CL will integrate it into
chevron button).  Chevron 4px from Omnibox or 2px from last browser
action, then 4px to wrench menu.  Chevron button has hover like other
buttons.

BUG=50575
TEST=Browser-actions area still works right WRT spacing and rearranging and everything else.

Review URL: http://codereview.chromium.org/3012044

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@54782 0039d316-1c4b-4281-b951-d872f2087c98