Update menu bitmaps when invoking window is set in wxOSX

Changing invoking window always needs to update the bitmaps because
the scale factor may need to be changed if this window is on a different
display, using different scaling, so do it automatically whenever
SetInvokingWindow() is called instead of having to remember to call
SetupBitmaps() manually everywhere SetInvokingWindow() is.

This required making the base class function virtual, but allows to get
rid of SetupBitmaps() call in wxWindow::DoPopupMenu(), as it can now
rely on this being already done by wxWindowBase::PopupMenu().

include/wx/menu.h

@@ -261,7 +261,7 @@ public:
     //
     // NB: avoid calling SetInvokingWindow() directly if possible, use
     //     wxMenuInvokingWindowSetter class below instead
-    void SetInvokingWindow(wxWindow *win);
+    virtual void SetInvokingWindow(wxWindow *win);
     wxWindow *GetInvokingWindow() const { return m_invokingWindow; }
 
     // the window associated with this menu: this is the invoking window for

include/wx/osx/menu.h

@@ -36,6 +36,8 @@ public:
 
     virtual void SetTitle(const wxString& title) wxOVERRIDE;
 
+    virtual void SetInvokingWindow(wxWindow* win) wxOVERRIDE;
+
     bool ProcessCommand(wxCommandEvent& event);
 
     // get the menu handle

src/osx/menu_osx.cpp

@@ -421,6 +421,14 @@ void wxMenu::Attach(wxMenuBarBase *menubar)
 }
 #endif
 
+void wxMenu::SetInvokingWindow(wxWindow* win)
+{
+    wxMenuBase::SetInvokingWindow(win);
+
+    if ( win )
+        SetupBitmaps();
+}
+
 void wxMenu::SetupBitmaps()
 {
     for ( wxMenuItemList::compatibility_iterator node = m_items.GetFirst();

src/osx/window_osx.cpp

@@ -871,8 +871,6 @@ bool wxWindowMac::SetCursor(const wxCursor& cursor)
 bool wxWindowMac::DoPopupMenu(wxMenu *menu, int x, int y)
 {
 #ifndef __WXUNIVERSAL__
-    menu->SetupBitmaps();
-
     if ( x == wxDefaultCoord && y == wxDefaultCoord )
     {
         wxPoint mouse = wxGetMousePosition();