[ash] Add TYPE_DIALOG and its item's LauncherContextMenu

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 ab41a4c4b22b737a87580830f89a9a2cf7c1027d..20e8fde871a1f51176dd950ed38647e2760bc874 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -158,7 +158,10 @@ aura::client::UserActionClient* ShellDelegateImpl::CreateUserActionClient() {
   return NULL;
 }
 
-ui::MenuModel* ShellDelegateImpl::CreateContextMenu(aura::Window* root) {
+ui::MenuModel* ShellDelegateImpl::CreateContextMenu(
+    aura::Window* root,
+    ash::ShelfItemDelegate* item_delegate,
+    ash::LauncherItem* item) {
   return new ContextMenu(root);
 }