Backed out 1 changesets (bug 1423869)for causing frequent Linux chrome failure in toolkit/content/tests/chrome/test_chromemargin.xul r=backout on a CLOSED TREE

Backed out changeset 4960f30d91b2 (bug 1423869)

widget/gtk/nsWindow.cpp

@@ -3795,8 +3795,7 @@ nsWindow::Create(nsIWidget* aParent,
          *    and we listen to the Gtk+ events on mContainer.
          */
         GtkStyleContext* style = gtk_widget_get_style_context(mShell);
-        drawToContainer =
-            (mIsCSDAvailable && GetCSDSupportLevel() == CSD_SUPPORT_FLAT) ||
+        drawToContainer = mIsCSDAvailable ||
                           gtk_style_context_has_class(style, "csd");
 #endif
         eventWidget = (drawToContainer) ? container : mShell;