Aura on Linux: Make a DesktopScreenX11 to match the windows one.

ui/aura/root_window_host_linux.h

Index: ui/aura/root_window_host_linux.h
diff --git a/ui/aura/root_window_host_linux.h b/ui/aura/root_window_host_linux.h
index ad5d61da5b44741b7cd264cc36fb37a20b8c7cfc..ae435e98fa7b2401c30a3b688626e0941de31bb9 100644
--- a/ui/aura/root_window_host_linux.h
+++ b/ui/aura/root_window_host_linux.h
@@ -16,6 +16,10 @@
 #include "ui/aura/root_window_host.h"
 #include "ui/gfx/rect.h"
 
+namespace ui {
+class ViewProp;
+}
+
 namespace aura {
 
 class RootWindowHostLinux : public RootWindowHost,
@@ -95,6 +99,8 @@ class RootWindowHostLinux : public RootWindowHost,
 
   scoped_array<XID> pointer_barriers_;
 
+  scoped_ptr<ui::ViewProp> prop_;
+
   DISALLOW_COPY_AND_ASSIGN(RootWindowHostLinux);
 };