ui: Cleanup class/struct forward declarations

ui/compositor/clip_recorder.h

 // Copyright 2015 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_COMPOSITOR_CLIP_RECORDER_H_
 #define UI_COMPOSITOR_CLIP_RECORDER_H_
 
 #include "base/macros.h"
 #include "ui/compositor/compositor_export.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace cc {
-class DisplayItem;
 class DisplayItemList;
 }
 
 namespace gfx {
 class Path;
 }
 
 namespace ui {
 class PaintContext;
 
@@ skipping 24 matching lines @@
   enum : int { kMaxOpCount = 4 };
   Closer closers_[kMaxOpCount];
   int num_closers_;
 
   DISALLOW_COPY_AND_ASSIGN(ClipRecorder);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_CLIP_RECORDER_H_