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..21f5050b89185b4908bbdb0b3714fe1e0a21629a 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"
@@ -432,6 +433,8 @@ void Shell::Init() {
 
   focus_cycler_.reset(new internal::FocusCycler());
 
+  message_center_.reset(new message_center::MessageCenter());
+
   screen_position_controller_.reset(new internal::ScreenPositionController);
   root_window_host_factory_.reset(delegate_->CreateRootWindowHostFactory());
   display_controller_.reset(new DisplayController);
@@ -839,6 +842,10 @@ aura::client::StackingClient* Shell::stacking_client() {
   return stacking_client_.get();
 }
 
+message_center::MessageCenter* Shell::message_center() {
+  return message_center_.get();
+}
+
 void Shell::InitRootWindowController(
     internal::RootWindowController* controller) {
   aura::RootWindow* root_window = controller->root_window();