Converts WindowTreeClientTest to be in terms of aura

ui/aura/mus/window_tree_client_delegate.h

 // Copyright 2014 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_MUS_WINDOW_TREE_CLIENT_DELEGATE_H_
 #define UI_AURA_MUS_WINDOW_TREE_CLIENT_DELEGATE_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 20 matching lines @@
   // InterfaceRequest.
   virtual void OnEmbed(std::unique_ptr<WindowTreeHostMus> window_tree_host) = 0;
 
   // Sent when another app is embedded in |root| (one of the roots of the
   // connection). Afer this call |root| is deleted. If the associated
   // WindowTreeClient was created from a WindowTreeClientRequest then
   // OnEmbedRootDestroyed() is called after the window is deleted.
   virtual void OnUnembed(Window* root);
 
   // Called when the embed root has been destroyed on the server side (or
-  // another client was embedded in the same window). This is only called if the
-  // WindowTreeClient was created from an InterfaceRequest. Generally when this
-  // is called the delegate should delete the WindowTreeClient.
-  virtual void OnEmbedRootDestroyed(Window* root) = 0;
+  // another client was embedded in the same window). This is called in two
+  // distinct cases:
+  // . If the WindowTreeClient was created from an InterfaceRequest. In this
+  //   case the WindowTreeClient associated with the WindowTreeHost is no
+  //   longer in a usable state and should be deleted (after deleting
+  //   |window_tree_host|).
+  // . When the window associated with a top level window (one created by way of
+  //   directly creating a WindowTreeHostMus) is destroyed on the server side.
+  //   In this case the |window_tree_host| should be destroyed, but the
+  //   WindowTreeClient is still usable.
+  virtual void OnEmbedRootDestroyed(WindowTreeHostMus* window_tree_host) = 0;
 
   // Called when the connection to the window server has been lost. After this
   // call the windows are still valid, and you can still do things, but they
   // have no real effect. Generally when this is called clients should delete
   // the corresponding WindowTreeClient.
   virtual void OnLostConnection(WindowTreeClient* client) = 0;
 
   // Called when the WindowTreeClient receives an input event observed via
   // StartPointerWatcher(). |target| may be null for events that were sent to
   // windows owned by other processes.
   virtual void OnPointerEventObserved(const ui::PointerEvent& event,
                                       Window* target) = 0;
 
   // Mus expects a single CaptureClient is used for all WindowTreeHosts. This
   // returns it. GetCaptureClient() is called from the constructor.
   virtual client::CaptureClient* GetCaptureClient() = 0;
 
   virtual PropertyConverter* GetPropertyConverter() = 0;
 
  protected:
   virtual ~WindowTreeClientDelegate() {}
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_TREE_CLIENT_DELEGATE_H_