mash: Migrate shelf menus to wm common types

ash/shell/shell_delegate_impl.cc

Index: ash/shell/shell_delegate_impl.cc
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index 7eb927e099281ffff57881bb267ce6721b870153..690e0fca8b8d53ca3ac3abe0512991bc1f967221 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -266,10 +266,9 @@ ShellDelegateImpl::CreatePointerWatcherDelegate() {
   return base::WrapUnique(new PointerWatcherDelegateAura);
 }
 
-ui::MenuModel* ShellDelegateImpl::CreateContextMenu(
-    ash::Shelf* shelf,
-    const ash::ShelfItem* item) {
-  return new ContextMenu(shelf);
+ui::MenuModel* ShellDelegateImpl::CreateContextMenu(WmShelf* wm_shelf,
+                                                    const ShelfItem* item) {
+  return new ContextMenu(wm_shelf);
 }
 
 GPUSupport* ShellDelegateImpl::CreateGPUSupport() {