Getting rid of SurfaceIdHandler as it is no longer needed.

ui/aura/mus/surface_id_handler.h

Index: ui/aura/mus/surface_id_handler.h
diff --git a/ui/aura/mus/surface_id_handler.h b/ui/aura/mus/surface_id_handler.h
deleted file mode 100644
index 4f5c8d34871467bf59554f474378ee800a7a449f..0000000000000000000000000000000000000000
--- a/ui/aura/mus/surface_id_handler.h
+++ /dev/null
@@ -1,32 +0,0 @@
-// Copyright 2016 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_SURFACE_ID_HANDLER_H_
-#define UI_AURA_MUS_SURFACE_ID_HANDLER_H_
-
-#include "cc/surfaces/surface_id.h"
-#include "ui/gfx/geometry/size.h"
-
-namespace cc {
-class SurfaceInfo;
-}
-
-namespace aura {
-
-class Window;
-
-class SurfaceIdHandler {
- public:
-  // Called when a child window allocates a new surface ID.
-  // If the handler wishes to retain ownership of the |surface_info|,
-  // it can move it. If a child's surface has been cleared then
-  // |surface_info| will refer to a null pointer.
-  virtual void OnChildWindowSurfaceChanged(
-      Window* window,
-      const cc::SurfaceInfo& surface_info) = 0;
-};
-
-}  // namespace aura
-
-#endif  // UI_AURA_MUS_SURFACE_ID_HANDLER_H_