Subtree caching implementation in blink-core

Source/core/paint/LayoutObjectDrawingRecorder.h

Index: Source/core/paint/LayoutObjectDrawingRecorder.h
diff --git a/Source/core/paint/LayoutObjectDrawingRecorder.h b/Source/core/paint/LayoutObjectDrawingRecorder.h
index cd79523f73d4eafbec90f131847e5889286f5cae..cdc59d7e685b9c7ebe83158737f5b57754a17fa6 100644
--- a/Source/core/paint/LayoutObjectDrawingRecorder.h
+++ b/Source/core/paint/LayoutObjectDrawingRecorder.h
@@ -23,7 +23,12 @@ public:
     {
         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)