aura-mus: Implement stacking in DesktopWindowTreeHostMus.

ui/aura/test/mus/change_completion_waiter.h

Index: ui/aura/test/mus/change_completion_waiter.h
diff --git a/ui/aura/test/mus/change_completion_waiter.h b/ui/aura/test/mus/change_completion_waiter.h
new file mode 100644
index 0000000000000000000000000000000000000000..bad862376e753fcefe699c2d14edb140749789fc
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+++ b/ui/aura/test/mus/change_completion_waiter.h
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+// Copyright 2017 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 UI_AURA_TEST_MUS_CHANGE_COMPLETION_WAITER_H_
+#define UI_AURA_TEST_MUS_CHANGE_COMPLETION_WAITER_H_
+
+#include "base/callback_forward.h"
+#include "base/run_loop.h"
+#include "ui/aura/mus/window_tree_client_test_observer.h"
+
+namespace aura {
+class WindowTreeClient;
+enum class ChangeType;
+
+namespace test {
+
+// A class which will Wait for next change of |type| to complete.
+class ChangeCompletionWaiter : public WindowTreeClientTestObserver {
+ public:
+  ChangeCompletionWaiter(WindowTreeClient* client,
+                         ChangeType type,
+                         bool success);
+  ~ChangeCompletionWaiter() override;
+
+  // Wait for the first change that occurred after construction of this object
+  // of |type| to complete. May return immediately if it's already done.
+  void Wait();
+
+ private:
+  // WindowTreeClientTestObserver:
+  void OnChangeStarted(uint32_t change_id,
+                       aura::ChangeType type) override;
+  void OnChangeCompleted(uint32_t change_id,
+                         aura::ChangeType type,
+                         bool success) override;
+
+  base::RunLoop run_loop_;
+  base::Closure quit_closure_;
+
+  enum class WaitState {
+    NOT_STARTED,
+    WAITING,
+    RECEIVED
+  } state_;
+
+  WindowTreeClient* client_;
+  aura::ChangeType type_;
+  uint32_t change_id_;
+  bool success_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChangeCompletionWaiter);
+};
+
+}  // namespace test
+}  // namespace aura
+
+#endif  // UI_AURA_TEST_MUS_CHANGE_COMPLETION_WAITER_H_