feat: enable Windows Control Overlay on Linux (#41769)

shell/browser/native_window_views.h

@@ -167,13 +167,9 @@ class NativeWindowViews : public NativeWindow,
 
 #if BUILDFLAG(IS_WIN)
   TaskbarHost& taskbar_host() { return taskbar_host_; }
+  void UpdateThickFrame();
 #endif
 
-#if BUILDFLAG(IS_WIN)
-  bool IsWindowControlsOverlayEnabled() const {
-    return (title_bar_style_ == NativeWindowViews::TitleBarStyle::kHidden) &&
-           titlebar_overlay_;
-  }
   SkColor overlay_button_color() const { return overlay_button_color_; }
   void set_overlay_button_color(SkColor color) {
     overlay_button_color_ = color;
@@ -183,9 +179,6 @@ class NativeWindowViews : public NativeWindow,
     overlay_symbol_color_ = color;
   }
 
-  void UpdateThickFrame();
-#endif
-
  private:
   // views::WidgetObserver:
   void OnWidgetActivationChanged(views::Widget* widget, bool active) override;
@@ -263,6 +256,10 @@ class NativeWindowViews : public NativeWindow,
   std::unique_ptr<EventDisabler> event_disabler_;
 #endif
 
+  // The color to use as the theme and symbol colors respectively for WCO.
+  SkColor overlay_button_color_ = SkColor();
+  SkColor overlay_symbol_color_ = SkColor();
+
 #if BUILDFLAG(IS_WIN)
 
   ui::WindowShowState last_window_state_;
@@ -306,11 +303,6 @@ class NativeWindowViews : public NativeWindow,
 
   std::optional<gfx::Rect> pending_bounds_change_;
 
-  // The color to use as the theme and symbol colors respectively for Window
-  // Controls Overlay if enabled on Windows.
-  SkColor overlay_button_color_;
-  SkColor overlay_symbol_color_;
-
   // The message ID of the "TaskbarCreated" message, sent to us when we need to
   // reset our thumbar buttons.
   UINT taskbar_created_message_ = 0;