Updates shadow when active window changes

components/mus/public/cpp/window_tree_connection.h

Index: components/mus/public/cpp/window_tree_connection.h
diff --git a/components/mus/public/cpp/window_tree_connection.h b/components/mus/public/cpp/window_tree_connection.h
index fc5b7db3675a76a38d8356db5aecfa0a6a891ef6..61897faed10a0ab610fb19c7499497e0a5c8ee9b 100644
--- a/components/mus/public/cpp/window_tree_connection.h
+++ b/components/mus/public/cpp/window_tree_connection.h
@@ -17,6 +17,7 @@ namespace mus {
 
 class Window;
 class WindowManagerDelegate;
+class WindowTreeConnectionObserver;
 class WindowTreeDelegate;
 
 // Encapsulates a connection to a window tree. A unique connection is made
@@ -67,6 +68,9 @@ class WindowTreeConnection {
 
   // Returns the id for this connection.
   virtual ConnectionSpecificId GetConnectionId() = 0;
+
+  virtual void AddObserver(WindowTreeConnectionObserver* observer) = 0;
+  virtual void RemoveObserver(WindowTreeConnectionObserver* observer) = 0;
 };
 
 }  // namespace mus