Pass shelf instances, not root windows, for ash context menus.

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 d996a2222f5d1dd92f427b0a1031c549311d398c..735397638e0e8313df7c019eda01137aa8ab4af3 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -225,9 +225,9 @@ ash::MediaDelegate* ShellDelegateImpl::CreateMediaDelegate() {
 }
 
 ui::MenuModel* ShellDelegateImpl::CreateContextMenu(
-    aura::Window* root_window,
+    ash::Shelf* shelf,
     const ash::ShelfItem* item) {
-  return new ContextMenu(root_window);
+  return new ContextMenu(shelf);
 }
 
 GPUSupport* ShellDelegateImpl::CreateGPUSupport() {