Ensure UI elements contrast with the right frame color.

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/optional.h"
 #include "base/win/registry.h"
 #include "chrome/browser/themes/theme_service.h"
 
 // Tracks updates to the native colors on Windows 10 and calcuates the values we
 // should use (which are not always what Windows uses). None of the values here
 // are relevant to earlier versions of Windows.
 class ThemeServiceWin : public ThemeService {
  public:
   ThemeServiceWin();
   ~ThemeServiceWin() override;
 
  private:
   // ThemeService:
   bool ShouldUseNativeFrame() const override;
   SkColor GetDefaultColor(int id, bool incognito) const override;
 
   // Returns true if colors from DWM can be used, i.e. this is a native frame
   // on Windows 10.
   bool DwmColorsAllowed() const;
 
   // Callback executed when |dwm_key_| is updated. This re-reads the active
   // frame color and updates |use_dwm_frame_color_|, |dwm_frame_color_| and
   // |dwm_inactive_frame_color_|.
   void OnDwmKeyUpdated();
 
   // Registry key containing the params that determine the DWM frame color.
   std::unique_ptr<base::win::RegKey> dwm_key_;
 
-  // True if the frame should be colored using the DWM values here. False if the
-  // default frame colors should be used instead.
-  bool use_dwm_frame_color_;
+  // The frame color when active. If empty the default colors should be used.
+  base::Optional<SkColor> dwm_frame_color_;
 
-  // The frame color when active.
-  SkColor dwm_frame_color_;
+  // True if we took dwm_inactive_frame_color_ from the registry (vs calculating
+  // it ourselves) and thus Windows will use it too.
+  bool inactive_frame_color_from_registry_;
 
-  // The frame color when inactive.
-  SkColor dwm_inactive_frame_color_;
+  // The frame color when inactive. If empty the default colors should be used.
+  base::Optional<SkColor> dwm_inactive_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_