Have Chrome draw top window border when using custom titlebar.

chrome/browser/themes/theme_service_win.h

Index: chrome/browser/themes/theme_service_win.h
diff --git a/chrome/browser/themes/theme_service_win.h b/chrome/browser/themes/theme_service_win.h
index a702f389417d92a2460c44840da4fafeffb4291b..78003bf5c254acba946203d37f4f8560a80b141b 100644
--- a/chrome/browser/themes/theme_service_win.h
+++ b/chrome/browser/themes/theme_service_win.h
@@ -33,6 +33,9 @@ class ThemeServiceWin : public ThemeService {
   // The DWM frame color, if available; white otherwise.
   SkColor dwm_frame_color_;
 
+  // The DWM accent border color, if available; white otherwise.
+  SkColor dwm_accent_color_;

[Bret, 2016/10/06 20:48:09]

Hmm this name is confusing because the AccentColor is actually the frame color,
even if it shows up in more limited circumstances than the border color. Maybe
just call it dwm_border_color_? Or maybe dwm_accent_border_color_ which is
consistent with what you're calling it everywhere else.

+
   DISALLOW_COPY_AND_ASSIGN(ThemeServiceWin);
 };