Simplify subtree (now subsequence) caching

Source/platform/graphics/paint/SubtreeRecorder.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 SubtreeRecorder_h
-#define SubtreeRecorder_h
-
-#include "platform/graphics/paint/DisplayItemClient.h"
-
-namespace blink {
-
-class DisplayItemList;
-class GraphicsContext;
-
-// Records subtree information during painting. The recorder's life span covers
-// all painting operations executed during the root of the subtree's paint method
-// for the paint phase.
-class PLATFORM_EXPORT SubtreeRecorder {
-public:
-    SubtreeRecorder(GraphicsContext&, const DisplayItemClientWrapper&, int paintPhase);
-    ~SubtreeRecorder();
-
-    bool canUseCache() const;
-
-private:
-    DisplayItemList* m_displayItemList;
-    DisplayItemClientWrapper m_client;
-    const int m_paintPhase;
-    bool m_canUseCache;
-#if ENABLE(ASSERT)
-    mutable bool m_checkedCanUseCache;
-#endif
-};
-
-} // namespace blink
-
-#endif // SubtreeRecorder_h