Change the visual appearance of panel on GTK per new UI design.

chrome/browser/ui/panels/native_panel.h

Index: chrome/browser/ui/panels/native_panel.h
diff --git a/chrome/browser/ui/panels/native_panel.h b/chrome/browser/ui/panels/native_panel.h
index 61d1ff92ad9d6f22f21b903f1e2ba374801d334a..527fbba5e834d9b310bb770d3eb6906ce9cd171a 100644
--- a/chrome/browser/ui/panels/native_panel.h
+++ b/chrome/browser/ui/panels/native_panel.h
@@ -101,12 +101,6 @@ class NativePanel {
 // native panel used only by test automation.
 class NativePanelTesting {
  public:
-  enum TitlebarButtonType {
-    CLOSE_BUTTON,
-    MINIMIZE_BUTTON,
-    RESTORE_BUTTON
-  };
-
   static NativePanelTesting* Create(NativePanel* native_panel);
   virtual ~NativePanelTesting() {}
 
@@ -136,7 +130,7 @@ class NativePanelTesting {
 
   virtual bool IsWindowSizeKnown() const = 0;
   virtual bool IsAnimatingBounds() const = 0;
-  virtual bool IsButtonVisible(TitlebarButtonType button_type) const = 0;
+  virtual bool IsButtonVisible(panel::TitlebarButtonType button_type) const = 0;
 };
 
 #endif  // CHROME_BROWSER_UI_PANELS_NATIVE_PANEL_H_