Restore NativeWidgetWin::OnSetIcon to eliminate classic theme titlebar flickering.

ui/views/widget/native_widget_win.h

Index: ui/views/widget/native_widget_win.h
diff --git a/ui/views/widget/native_widget_win.h b/ui/views/widget/native_widget_win.h
index f0cbfbd29605e5aed1eb69f5d94ed9fd889b263d..006213237fc20a73345e5708bd5f29169a09ffd0 100644
--- a/ui/views/widget/native_widget_win.h
+++ b/ui/views/widget/native_widget_win.h
@@ -361,6 +361,7 @@ class VIEWS_EXPORT NativeWidgetWin : public ui::WindowImpl,
     MSG_WM_PAINT(OnPaint)
     MSG_WM_POWERBROADCAST(OnPowerBroadcast)
     MSG_WM_SETFOCUS(OnSetFocus)
+    MSG_WM_SETICON(OnSetIcon)
     MSG_WM_SETTEXT(OnSetText)
     MSG_WM_SETTINGCHANGE(OnSettingChange)
     MSG_WM_SIZE(OnSize)
@@ -427,6 +428,7 @@ class VIEWS_EXPORT NativeWidgetWin : public ui::WindowImpl,
   virtual LRESULT OnReflectedMessage(UINT msg, WPARAM w_param, LPARAM l_param);
   virtual LRESULT OnSetCursor(UINT message, WPARAM w_param, LPARAM l_param);
   virtual void OnSetFocus(HWND old_focused_window);
+  virtual LRESULT OnSetIcon(UINT size_type, HICON new_icon);
   virtual LRESULT OnSetText(const wchar_t* text);
   virtual void OnSettingChange(UINT flags, const wchar_t* section);
   virtual void OnSize(UINT param, const CSize& size);