mash: Migrate shelf app list button to wm common types

ash/test/shell_test_api.cc

Index: ash/test/shell_test_api.cc
diff --git a/ash/test/shell_test_api.cc b/ash/test/shell_test_api.cc
index f64bc305d958d2e8d23d6510d366e0f9f2973f4b..457d201f97d5f0fb2dfa3cf7075a32c0b4635eec 100644
--- a/ash/test/shell_test_api.cc
+++ b/ash/test/shell_test_api.cc
@@ -34,7 +34,8 @@ AshNativeCursorManager* ShellTestApi::ash_native_cursor_manager() {
 }
 
 ShelfModel* ShellTestApi::shelf_model() {
-  return shell_->shelf_model_.get();
+  // TODO(jamescook): Remove this and access WmShell::shelf_model() directly.
+  return shell_->wm_shell_->shelf_model();
 }
 
 DragDropController* ShellTestApi::drag_drop_controller() {