WIP: Eliminate event.target() usage from TrayEventFilter

components/mus/public/cpp/window_tree_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 COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_DELEGATE_H_
 #define COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_DELEGATE_H_
 
 #include <string>
 
 #include "components/mus/public/interfaces/window_tree.mojom.h"
@@ skipping 34 matching lines @@
   // and the connection is configured to delete when there are no roots (the
   // default), then after |root| is destroyed the connection is destroyed as
   // well.
   virtual void OnUnembed(Window* root);
 
   // Called from the destructor of WindowTreeConnection after all the Windows
   // have been destroyed. |connection| is no longer valid after this call.
   virtual void OnConnectionLost(WindowTreeConnection* connection) = 0;
 
   // Called when the WindowTreeConnection receives an input event observed via
-  // SetEventObserver().
-  virtual void OnEventObserved(const ui::Event& event) = 0;
+  // SetEventObserver(). |target| may be null for events that were sent to
+  // windows owned by other processes.
+  virtual void OnEventObserved(const ui::Event& event,
+                               Window* target) = 0;
 
  protected:
   virtual ~WindowTreeDelegate() {}
 };
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_DELEGATE_H_