Handle high resolution displays in wxBitmapButtonBase::NewCloseButton().

Bitmap for the close button is scaled based on GetContentScaleFactor(). On OS X the resulting bitmap has to use the correct scaling factor in order to be displayed correctly on the button when using a high resolution display.

src/common/bmpbtncmn.cpp

@@ -103,13 +103,21 @@ GetCloseButtonBitmap(wxWindow *win,
                      const wxColour& colBg,
                      int flags = 0)
 {
-    wxBitmap bmp(size);
+    wxSize drawSize = size * win->GetContentScaleFactor();
+
+    wxBitmap bmp(drawSize);
     wxMemoryDC dc(bmp);
     dc.SetBackground(colBg);
     dc.Clear();
+
+
     wxRendererNative::Get().
-        DrawTitleBarBitmap(win, dc, size, wxTITLEBAR_BUTTON_CLOSE, flags);
+        DrawTitleBarBitmap(win, dc, drawSize, wxTITLEBAR_BUTTON_CLOSE, flags);
+#ifdef __WXOSX__
+    return wxBitmap(bmp.CreateCGImage(), win->GetContentScaleFactor());
+#else
     return bmp;
+#endif
 }
 
 #endif // wxHAS_DRAW_TITLE_BAR_BITMAP