Subtree caching implementation in blink-core

Source/core/paint/LayoutObjectDrawingRecorder.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 LayoutObjectDrawingRecorder_h
 #define LayoutObjectDrawingRecorder_h
 
 #include "core/layout/LayoutObject.h"
 #include "core/paint/PaintPhase.h"
 #include "platform/geometry/LayoutRect.h"
 #include "platform/graphics/paint/DisplayItemCacheSkipper.h"
 #include "platform/graphics/paint/DrawingRecorder.h"
 #include "wtf/Optional.h"
 
 namespace blink {
 
 class GraphicsContext;
 
 // Convenience wrapper of DrawingRecorder for LayoutObject painters.
 class LayoutObjectDrawingRecorder final {
 public:
     static bool useCachedDrawingIfPossible(GraphicsContext& context, const LayoutObject& layoutObject, DisplayItem::Type displayItemType)
     {
         if (layoutObject.fullPaintInvalidationReason() == PaintInvalidationDelayedFull)
             return false;
-        return DrawingRecorder::useCachedDrawingIfPossible(context, layoutObject, displayItemType);
+        // TODO(wangxianzhu): Use LayoutObject repaint flags when possible to avoid hash lookups in DisplayItemList.
+        if (DrawingRecorder::useCachedDrawingIfPossible(context, layoutObject, displayItemType)) {
+            ASSERT(!layoutObject.selfNeedsRepaint());
+            return true;
+        }
+        return false;
     }
 
     static bool useCachedDrawingIfPossible(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase)
     {
         return useCachedDrawingIfPossible(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase));
     }
 
     LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, DisplayItem::Type displayItemType, const FloatRect& clip)
     {
         // We may paint a delayed-invalidation object before it's actually invalidated.
@@ skipping 13 matching lines @@
 #endif
 
 private:
     Optional<DisplayItemCacheSkipper> m_cacheSkipper;
     Optional<DrawingRecorder> m_drawingRecorder;
 };
 
 } // namespace blink
 
 #endif // LayoutObjectDrawingRecorder_h