Support creation of toplevel mus::Windows on separate displays

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>
 
 #include "base/macros.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "ui/display/display.h"
 #include "ui/wm/public/window_types.h"
 
 namespace display {
 class Display;
 }
 
 namespace gfx {
 class Rect;
 }
 
@@ skipping 28 matching lines @@
   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);
-  ui::Window* CreateFullscreenTestWindow();
+
+  // Creates a visibile fullscreen top level window on the display corresponding
+  // to the display_id provided.
+  ui::Window* CreateFullscreenTestWindow(
+      int64_t display_id = display::kInvalidDisplayId);
 
   // 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_