Add simple mash context menu support.

ash/mus/shell_delegate_mus.cc

Index: ash/mus/shell_delegate_mus.cc
diff --git a/ash/mus/shell_delegate_mus.cc b/ash/mus/shell_delegate_mus.cc
index 7f627e10078486acc7b5b6144b3fb5ddc60cc243..a8a39e96bcf78d9d50ec21e08b61d6522680273f 100644
--- a/ash/mus/shell_delegate_mus.cc
+++ b/ash/mus/shell_delegate_mus.cc
@@ -8,6 +8,7 @@
 #include "ash/default_user_wallpaper_delegate.h"
 #include "ash/gpu_support_stub.h"
 #include "ash/media_delegate.h"
+#include "ash/mus/context_menu_mus.h"
 #include "ash/mus/shelf_delegate_mus.h"
 #include "ash/session/session_state_delegate.h"
 #include "ash/system/tray/default_system_tray_delegate.h"
@@ -94,7 +95,9 @@ class MediaDelegateStub : public MediaDelegate {
 
 }  // namespace
 
-ShellDelegateMus::ShellDelegateMus() {}
+ShellDelegateMus::ShellDelegateMus(mojo::Connector* connector)
+    : connector_(connector) {}
+
 ShellDelegateMus::~ShellDelegateMus() {}
 
 bool ShellDelegateMus::IsFirstRunAfterBoot() const {
@@ -199,8 +202,9 @@ MediaDelegate* ShellDelegateMus::CreateMediaDelegate() {
 
 ui::MenuModel* ShellDelegateMus::CreateContextMenu(ash::Shelf* shelf,
                                                    const ShelfItem* item) {
-  NOTIMPLEMENTED();
-  return nullptr;
+  scoped_ptr<ContextMenuMus> menu(new ContextMenuMus(nullptr, shelf, item));
+  menu->InitializeRootMenu(connector_);
+  return menu.release();
 }
 
 GPUSupport* ShellDelegateMus::CreateGPUSupport() {