OSX: Reduce the internal right padding of -webkit-appearance:menulist-button.

- Remove paddingBeforeSeparator.
  We remove the separator a long time ago.

- Shrink menuListArrowPadding{Left,Right}
  New value matches to the native appearance in Yosemite.

This CL has small compatibility risk.  This CL makes the intrinsic width of menulist
<select> different in -webkit-appearance:menulist and -webkit-appearnace:
menulist-button.  It means specifying background-color CSS property to <select> may
change its width.

BUG=558326

Review URL: https://codereview.chromium.org/1474943003

Cr-Commit-Position: refs/heads/master@{#361641}
5 files changed