mash: Port mojo:ash_sysui's ContextMenuMus to mojo:ash.

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 285e1a7fc05ba109ee43bf4785d2e51a3d8834ff..a81da934cff327035ff51ed375bbec3cfbe0a83e 100644
--- a/ash/mus/shell_delegate_mus.cc
+++ b/ash/mus/shell_delegate_mus.cc
@@ -13,6 +13,7 @@
 #include "ash/common/shelf/shelf_delegate.h"
 #include "ash/common/system/tray/default_system_tray_delegate.h"
 #include "ash/mus/accessibility_delegate_mus.h"
+#include "ash/mus/context_menu_mus.h"
 #include "ash/mus/new_window_delegate_mus.h"
 #include "base/memory/ptr_util.h"
 #include "base/strings/string16.h"
@@ -200,7 +201,7 @@ SystemTrayDelegate* ShellDelegateMus::CreateSystemTrayDelegate() {
   return new DefaultSystemTrayDelegate;
 }
 
-UserWallpaperDelegate* ShellDelegateMus::CreateUserWallpaperDelegate() {
+WallpaperDelegate* ShellDelegateMus::CreateWallpaperDelegate() {
   NOTIMPLEMENTED();
   return nullptr;
 }
@@ -230,8 +231,7 @@ std::unique_ptr<PaletteDelegate> ShellDelegateMus::CreatePaletteDelegate() {
 
 ui::MenuModel* ShellDelegateMus::CreateContextMenu(WmShelf* wm_shelf,
                                                    const ShelfItem* item) {
-  NOTIMPLEMENTED();
-  return nullptr;
+  return new ContextMenuMus(wm_shelf);
 }
 
 GPUSupport* ShellDelegateMus::CreateGPUSupport() {