b=521940 don't paint the plugin socket window to avoid flicker on load r=roc

--HG--
extra : rebase_source : 9a0f5cf10ecd3c939e6f13c14c9bcd88ace5d457

modules/plugin/base/src/nsPluginNativeWindowGtk2.cpp

@@ -261,6 +261,13 @@ nsresult nsPluginNativeWindowGtk2::CreateXEmbedWindow() {
   gtk_container_add(container, mSocketWidget);
   gtk_widget_realize(mSocketWidget);
 
+  // The GtkSocket has a visible window, but the plugin's XEmbed plug will
+  // cover this window.  Normally GtkSockets let the X server paint their
+  // background and this would happen immediately (before the plug is
+  // created).  Setting the background to None prevents the server from
+  // painting this window, avoiding flicker.
+  gdk_window_set_back_pixmap(mSocketWidget->window, NULL, FALSE);
+
   // Resize before we show
   SetAllocation();
 

widget/src/gtkxtbin/gtk2xtbin.c

@@ -387,6 +387,15 @@ gtk_xtbin_new (GdkWindow *parent_window, String * f)
   if (user_data)
     gtk_container_add(GTK_CONTAINER(user_data), GTK_WIDGET(xtbin));
 
+  /* This GtkSocket has a visible window, but the Xt plug will cover this
+   * window.  Normally GtkSockets let the X server paint their background and
+   * this would happen immediately (before the plug is mapped).  Setting the
+   * background to None prevents the server from painting this window,
+   * avoiding flicker.
+   */
+  gtk_widget_realize(GTK_WIDGET(xtbin));
+  gdk_window_set_back_pixmap(GTK_WIDGET(xtbin)->window, NULL, FALSE);
+
   return GTK_WIDGET (xtbin);
 }