Implement SetShape() for wxPopupWindow in wxGTK.

Move SetShape() implementation from wxTopLevelWindow to wxNonOwnedWindow so
that wxPopupWindow, which also inherits from the latter, could use it as well.

This makes it possible to have popup windows with irregular shapes in wxGTK as
well as in wxMSW and wxOSX.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69408 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/toplevel.h

@@ -57,8 +57,6 @@ public:
     virtual bool ShowFullScreen(bool show, long style = wxFULLSCREEN_ALL);
     virtual bool IsFullScreen() const { return m_fsIsShowing; };
 
-    virtual bool SetShape(const wxRegion& region);
-
     virtual void RequestUserAttention(int flags = wxUSER_ATTENTION_INFO);
 
     virtual void SetWindowStyleFlag( long style );
@@ -113,9 +111,6 @@ public:
     // size of WM decorations
     wxSize m_decorSize;
 
-    // shape of the frame
-    wxRegion m_shape;
-
     // private gtk_timeout_add result for mimicing wxUSER_ATTENTION_INFO and
     // wxUSER_ATTENTION_ERROR difference, -2 for no hint, -1 for ERROR hint, rest for GtkTimeout handle.
     int m_urgency_hint;