Implement the algorithm to test merging and overlap in PaintArtifactCompositor.

third_party/WebKit/Source/platform/graphics/paint/PaintController.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 PaintController_h
 #define PaintController_h
 
 #include "platform/PlatformExport.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/geometry/IntRect.h"
@@ skipping 224 matching lines @@
                               : m_currentPaintArtifact.getDisplayItemList()
                                     .usedCapacityInBytes());
     }
   }
 
   // Set new item state (cache skipping, etc) for a new item.
   void processNewItem(DisplayItem&);
   DisplayItem& moveItemFromCurrentListToNewList(size_t);
 
   void showDebugDataInternal(bool showPictures) const;
-  String displayItemListAsDebugString(const DisplayItemList&,
-                                      bool showPictures) const;
 
   // Maps clients to indices of display items or chunks of each client.
   using IndicesByClientMap = HashMap<const DisplayItemClient*, Vector<size_t>>;
 
   static size_t findMatchingItemFromIndex(const DisplayItem::Id&,
                                           const IndicesByClientMap&,
                                           const DisplayItemList&);
   static void addItemToIndexIfNeeded(const DisplayItem&,
                                      size_t index,
                                      IndicesByClientMap&);
@@ skipping 122 matching lines @@
 
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
   // A stack recording subsequence clients that are currently painting.
   Vector<const DisplayItemClient*> m_currentSubsequenceClients;
 #endif
 };
 
 }  // namespace blink
 
 #endif  // PaintController_h