The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/944eab72bd2c478b03195680ef033b1d88aa85cc

commit 944eab72bd2c478b03195680ef033b1d88aa85cc
Author: estade <estade@chromium.org>
Date: Mon Apr 17 16:39:06 2017

Use NativeTheme to draw vertical menu separators.

Use NativeTheme to draw vertical menu separators ("menu button border")
so that they look like native horizontal separators instead of being
subtly different.

For now the GTK theme doesn't have a way to draw vertical separators,
so the old way of doing things (SkCanvas::drawRect) is retained, just
moved from app_menu.cc to native_theme_gtk3.cc.

BUG= 710159 
TBR=sadrul@chromium.org

Review-Url: https://codereview.chromium.org/2813703003
Cr-Commit-Position: refs/heads/master@{#464930}

[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/chrome/browser/ui/libgtkui/native_theme_gtk2.cc
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/chrome/browser/ui/libgtkui/native_theme_gtk3.cc
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/chrome/browser/ui/views/toolbar/app_menu.cc
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/ui/base/models/menu_separator_types.h
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/ui/native_theme/common_theme.cc
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/ui/native_theme/native_theme.h
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/ui/native_theme/native_theme_dark_aura.cc
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/ui/native_theme/native_theme_mac.mm
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/ui/native_theme/native_theme_win.cc
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/ui/native_theme/native_theme_win.h
[modify] https://crrev.com/944eab72bd2c478b03195680ef033b1d88aa85cc/ui/views/controls/menu/menu_separator.cc

we'll still need to do some work for various scale factors, but at least the vertical and horizontal separators are now the same.