Avoid re-iterate out-of-order display items

Source/platform/graphics/paint/DisplayItemList.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 DisplayItemList_h
 #define DisplayItemList_h
 
 #include "platform/PlatformExport.h"
 #include "platform/graphics/ContiguousContainer.h"
 #include "platform/graphics/paint/DisplayItem.h"
@@ skipping 123 matching lines @@
 #ifndef NDEBUG
     WTF::String displayItemsAsDebugString(const DisplayItems&) const;
 #endif
 
     // Indices into PaintList of all DrawingDisplayItems and BeginSubtreeDisplayItems of each client.
     // Temporarily used during merge to find out-of-order display items.
     using DisplayItemIndicesByClientMap = HashMap<DisplayItemClient, Vector<size_t>>;
 
     static size_t findMatchingItemFromIndex(const DisplayItem::Id&, const DisplayItemIndicesByClientMap&, const DisplayItems&);
     static void addItemToIndexIfNeeded(const DisplayItem&, size_t index, DisplayItemIndicesByClientMap&);
-    DisplayItems::iterator findOutOfOrderCachedItem(DisplayItems::iterator currentIt, const DisplayItem::Id&, DisplayItemIndicesByClientMap&);
-    DisplayItems::iterator findOutOfOrderCachedItemForward(DisplayItems::iterator currentIt, const DisplayItem::Id&, DisplayItemIndicesByClientMap&);
+
+    struct OutOfOrderIndexContext;
+    DisplayItems::iterator findOutOfOrderCachedItem(DisplayItems::iterator currentIt, const DisplayItem::Id&, OutOfOrderIndexContext&);
+    DisplayItems::iterator findOutOfOrderCachedItemForward(const DisplayItem::Id&, OutOfOrderIndexContext&);
     void copyCachedSubtree(DisplayItems::iterator& currentIt, DisplayItems& updatedList);
 
 #if ENABLE(ASSERT)
     // The following two methods are for checking under-invalidations
     // (when RuntimeEnabledFeatures::slimmingPaintUnderInvalidationCheckingEnabled).
     void checkCachedDisplayItemIsUnchanged(const DisplayItem&, DisplayItemIndicesByClientMap&);
     void checkNoRemainingCachedDisplayItems();
 #endif
 
     void replay(GraphicsContext&);
@@ skipping 23 matching lines @@
     // This is used to check duplicated ids during add(). We could also check during
     // updatePaintList(), but checking during add() helps developer easily find where
     // the duplicated ids are from.
     DisplayItemIndicesByClientMap m_newDisplayItemIndicesByClient;
 #endif
 };
 
 } // namespace blink
 
 #endif // DisplayItemList_h