Add child for parent_mus when params.parent_mus is not initialized.

ash/mus/test/wm_test_base.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_MUS_TEST_WM_TEST_BASE_H_
 #define ASH_MUS_TEST_WM_TEST_BASE_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 30 matching lines @@
   // TODO(sky): temporary until http://crbug.com/611563 is fixed.
   bool SupportsMultipleDisplays() const;
 
   // Update the display configuration as given in |display_spec|.
   // See test::DisplayManagerTestApi::UpdateDisplay for more details.
   void UpdateDisplay(const std::string& display_spec);
 
   ui::Window* GetPrimaryRootWindow();
   ui::Window* GetSecondaryRootWindow();
 
+  RootWindowController* GetPrimaryRootWindowController();
+  RootWindowController* GetSecondaryRootWindowController();
+
   display::Display GetPrimaryDisplay();
   display::Display GetSecondaryDisplay();
 
   // Creates a top level window visible window in the appropriate container.
   // NOTE: you can explicitly destroy the returned value if necessary, but it
   // will also be automatically destroyed when the WindowTreeClient is
   // destroyed.
   ui::Window* CreateTestWindow(const gfx::Rect& bounds);
   ui::Window* CreateTestWindow(const gfx::Rect& bounds,
                                ui::wm::WindowType window_type);
+
+  // for multiple displays
+  ui::Window* CreateTestWindow(const gfx::Rect& bounds,
+                               ui::wm::WindowType window_type,
+                               RootWindowController* root);
+
   ui::Window* CreateFullscreenTestWindow();
+  ui::Window* CreateFullscreenTestWindow(RootWindowController* root);
 
   // Creates a window parented to |parent|. The returned window is visible.
   ui::Window* CreateChildTestWindow(ui::Window* parent,
                                     const gfx::Rect& bounds);
 
  protected:
   // testing::Test:
   void SetUp() override;
   void TearDown() override;
 
  private:
   friend class AshTestImplMus;
 
   bool setup_called_ = false;
   bool teardown_called_ = false;
   std::unique_ptr<WmTestHelper> test_helper_;
 
   DISALLOW_COPY_AND_ASSIGN(WmTestBase);
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_TEST_WM_TEST_BASE_H_