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 - Changing button and separator height to 32px.
 - Changing separator margin to 16px.
 - Removing obsolete logic to use a negative margin for non primary buttons.
   It is obsolete since both types of buttons now have a border and they can
   use the same amount of margin.

Bug: 841858,832173
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I1b3bf0d5a7f6b4e81bc5e25a16b422a54487214b
Reviewed-on: https://chromium-review.googlesource.com/1054552Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558075}