Start delegating notifications to MessageCenter on Windows.

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index f1c6d99f55562cf29377defba9e35eedcfc2c332..bce9e41f9ec7d92e98f217bdd73b94cb3d33c5b4 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -85,6 +85,7 @@
 #include "ui/gfx/image/image_skia.h"
 #include "ui/gfx/screen.h"
 #include "ui/gfx/size.h"
+#include "ui/message_center/message_center.h"
 #include "ui/views/corewm/compound_event_filter.h"
 #include "ui/views/corewm/corewm_switches.h"
 #include "ui/views/corewm/focus_controller.h"
@@ -839,6 +840,12 @@ aura::client::StackingClient* Shell::stacking_client() {
   return stacking_client_.get();
 }
 
+message_center::MessageCenter* Shell::message_center() {
+  if (!message_center_.get())
+    message_center_.reset(new message_center::MessageCenter());
+  return message_center_.get();
+}
+
 void Shell::InitRootWindowController(
     internal::RootWindowController* controller) {
   aura::RootWindow* root_window = controller->root_window();