Put back the code that I accidentally removed in crrev.com/17099003

ui/aura/root_window_host_x11.cc

Index: ui/aura/root_window_host_x11.cc
diff --git a/ui/aura/root_window_host_x11.cc b/ui/aura/root_window_host_x11.cc
index 858abbc205d81d6beb1fec866ae106e85fb31119..d0709cc0530b0deaf5c525e6a9283f49e4ee1d0a 100644
--- a/ui/aura/root_window_host_x11.cc
+++ b/ui/aura/root_window_host_x11.cc
@@ -413,6 +413,9 @@ RootWindowHostX11::RootWindowHostX11(const gfx::Rect& bounds)
                   32,
                   PropModeReplace,
                   reinterpret_cast<unsigned char*>(&pid), 1);
+
+  XRRSelectInput(xdisplay_, x_root_window_,
+                 RRScreenChangeNotifyMask | RROutputChangeNotifyMask);
   Env::GetInstance()->AddObserver(this);
 }