Updates shadow when active window changes

components/mus/public/cpp/window_tree_connection.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 COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_H_
 #define COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "components/mus/common/types.h"
 #include "components/mus/public/interfaces/window_tree.mojom.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 
 namespace mus {
 
 class Window;
 class WindowManagerDelegate;
+class WindowTreeConnectionObserver;
 class WindowTreeDelegate;
 
 // Encapsulates a connection to a window tree. A unique connection is made
 // every time an app is embedded.
 class WindowTreeConnection {
  public:
   enum class CreateType {
     // Indicates Create() should wait for OnEmbed(). If true, the
     // WindowTreeConnection returned from Create() will have its root, otherwise
     // the WindowTreeConnection will get the root at a later time.
@@ skipping 30 matching lines @@
   // Windows are initially hidden, use SetVisible(true) to show.
   Window* NewWindow() { return NewWindow(nullptr); }
   virtual Window* NewWindow(
       const std::map<std::string, std::vector<uint8_t>>* properties) = 0;
 
   // Returns true if ACCESS_POLICY_EMBED_ROOT was specified.
   virtual bool IsEmbedRoot() = 0;
 
   // Returns the id for this connection.
   virtual ConnectionSpecificId GetConnectionId() = 0;
+
+  virtual void AddObserver(WindowTreeConnectionObserver* observer) = 0;
+  virtual void RemoveObserver(WindowTreeConnectionObserver* observer) = 0;
 };
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_H_