Simplify subtree (now subsequence) caching

Source/platform/graphics/paint/SubtreeRecorder.cpp

Index: Source/platform/graphics/paint/SubtreeRecorder.cpp
diff --git a/Source/platform/graphics/paint/SubtreeRecorder.cpp b/Source/platform/graphics/paint/SubtreeRecorder.cpp
deleted file mode 100644
index 5cc1e8caf64f7784318d66d3480247c9ab8fd53c..0000000000000000000000000000000000000000
--- a/Source/platform/graphics/paint/SubtreeRecorder.cpp
+++ /dev/null
@@ -1,58 +0,0 @@
-// 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.
-
-#include "config.h"
-#include "platform/graphics/paint/SubtreeRecorder.h"
-
-#include "platform/RuntimeEnabledFeatures.h"
-#include "platform/graphics/GraphicsContext.h"
-#include "platform/graphics/paint/CachedDisplayItem.h"
-#include "platform/graphics/paint/DisplayItemList.h"
-#include "platform/graphics/paint/SubtreeDisplayItem.h"
-
-namespace blink {
-
-SubtreeRecorder::SubtreeRecorder(GraphicsContext& context, const DisplayItemClientWrapper& client, int paintPhase)
-    : m_displayItemList(context.displayItemList())
-    , m_client(client)
-    , m_paintPhase(paintPhase)
-    , m_canUseCache(false)
-#if ENABLE(ASSERT)
-    , m_checkedCanUseCache(false)
-#endif
-{
-    if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
-        return;
-
-    ASSERT(m_displayItemList);
-
-    // TODO(wangxianzhu): Implement subtree caching.
-
-    if (!m_canUseCache)
-        m_displayItemList->createAndAppend<BeginSubtreeDisplayItem>(m_client, DisplayItem::paintPhaseToBeginSubtreeType(paintPhase));
-}
-
-SubtreeRecorder::~SubtreeRecorder()
-{
-    if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
-        return;
-
-    ASSERT(m_checkedCanUseCache);
-    if (m_canUseCache)
-        m_displayItemList->createAndAppend<CachedDisplayItem>(m_client, DisplayItem::paintPhaseToCachedSubtreeType(m_paintPhase));
-    else if (m_displayItemList->lastDisplayItemIsNoopBegin())
-        m_displayItemList->removeLastDisplayItem();
-    else
-        m_displayItemList->createAndAppend<EndSubtreeDisplayItem>(m_client, DisplayItem::paintPhaseToEndSubtreeType(m_paintPhase));
-}
-
-bool SubtreeRecorder::canUseCache() const
-{
-#if ENABLE(ASSERT)
-    m_checkedCanUseCache = true;
-#endif
-    return m_canUseCache;
-}
-
-} // namespace blink