Clean up ash::ShellTestApi

ash/wm/dock/docked_window_resizer_unittest.cc

Index: ash/wm/dock/docked_window_resizer_unittest.cc
diff --git a/ash/wm/dock/docked_window_resizer_unittest.cc b/ash/wm/dock/docked_window_resizer_unittest.cc
index d9b3b2a476f2faf1e235f7e0839079ed6cf3d1f1..da018ecc58055a7b37a8626c595a2346931ba7c3 100644
--- a/ash/wm/dock/docked_window_resizer_unittest.cc
+++ b/ash/wm/dock/docked_window_resizer_unittest.cc
@@ -13,6 +13,7 @@
 #include "ash/common/wm/panels/panel_layout_manager.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/common/wm/wm_event.h"
+#include "ash/common/wm_shell.h"
 #include "ash/display/window_tree_host_manager.h"
 #include "ash/root_window_controller.h"
 #include "ash/screen_util.h"
@@ -22,7 +23,6 @@
 #include "ash/shell.h"
 #include "ash/test/ash_test_base.h"
 #include "ash/test/cursor_manager_test_api.h"
-#include "ash/test/shell_test_api.h"
 #include "ash/test/test_shelf_delegate.h"
 #include "ash/wm/drag_window_resizer.h"
 #include "ash/wm/window_state_aura.h"
@@ -51,8 +51,7 @@ class DockedWindowResizerTest
   void SetUp() override {
     AshTestBase::SetUp();
     UpdateDisplay("600x400");
-    test::ShellTestApi test_api(Shell::GetInstance());
-    model_ = test_api.shelf_model();
+    model_ = WmShell::Get()->shelf_model();
   }
 
   void TearDown() override { AshTestBase::TearDown(); }