[ash] Add TYPE_DIALOG and its item's LauncherContextMenu

ash/shelf/shelf_window_watcher_item_delegate.cc

Index: ash/shelf/shelf_window_watcher_item_delegate.cc
diff --git a/ash/shelf/shelf_window_watcher_item_delegate.cc b/ash/shelf/shelf_window_watcher_item_delegate.cc
index 6c7cc6565dcfda44f1298be9f9b0614ddaaed7b0..99b57c529243b5ec765649c129c898bf920ac743 100644
--- a/ash/shelf/shelf_window_watcher_item_delegate.cc
+++ b/ash/shelf/shelf_window_watcher_item_delegate.cc
@@ -4,6 +4,7 @@
 
 #include "ash/shelf/shelf_window_watcher_item_delegate.h"
 
+#include "ash/shelf/shelf_item_context_menu.h"
 #include "ash/shelf/shelf_util.h"
 #include "ash/wm/window_state.h"
 #include "ui/aura/window.h"
@@ -47,8 +48,7 @@ base::string16 ShelfWindowWatcherItemDelegate::GetTitle() {
 
 ui::MenuModel* ShelfWindowWatcherItemDelegate::CreateContextMenu(
     aura::Window* root_window) {
-  // TODO(simonhong): Create ShelfItemContextMenu.
-  return NULL;
+  return new ShelfItemContextMenu(this, root_window);
 }
 
 ShelfMenuModel* ShelfWindowWatcherItemDelegate::CreateApplicationMenu(