Fix app menu borders for RTL
Fix app menu borders for RTL

BUG=612485
TEST=Set to RTL language, open main browser (app) menu, observe that
button separators in Zoom and Edit rows are properly placed, e.g.

[ ]  |  +  100%  -  |   Zoom

Paste | Copy | Cut |   Edit

Review-Url: https://codereview.chromium.org/1988983004
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#394850}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk