Have Chrome draw top window border when using custom titlebar.

chrome/browser/themes/theme_service_win.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_THEMES_THEME_SERVICE_WIN_H_
 #define CHROME_BROWSER_THEMES_THEME_SERVICE_WIN_H_
 
 #include "base/win/registry.h"
 #include "chrome/browser/themes/theme_service.h"
 
@@ skipping 15 matching lines @@
   // frame color and updates |dwm_frame_color_|.
   void OnDwmKeyUpdated();
 
   // Registry key containing the params that determine the DWM frame color.
   // This is only initialized on Windows 10.
   std::unique_ptr<base::win::RegKey> dwm_key_;
 
   // The DWM frame color, if available; white otherwise.
   SkColor dwm_frame_color_;
 
+  // The DWM accent border color, if available; white otherwise.
+  SkColor dwm_accent_border_color_;
+
   DISALLOW_COPY_AND_ASSIGN(ThemeServiceWin);
 };
 
 #endif  // CHROME_BROWSER_THEMES_THEME_SERVICE_WIN_H_