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 7c940d4198d00bc29e1a2ac66d01f46963749b06..2d39516b9272202ba227df9da0f91bdd362e138f 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -83,6 +83,7 @@
 #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"
@@ -830,6 +831,12 @@ void Shell::DoInitialWorkspaceAnimation() {
       DoInitialAnimation();
 }
 
+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();