Implement the algorithm to test merging and overlap in PaintArtifactCompositor.

third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h

 // 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.
 
 #ifndef PaintChunker_h
 #define PaintChunker_h
 
 #include "platform/PlatformExport.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "platform/graphics/paint/PaintChunk.h"
@@ skipping 55 matching lines @@
     DefaultBehavior = 0,
 
     // Item requires its own paint chunk.
     RequiresSeparateChunk,
   };
 
   Vector<PaintChunk> m_chunks;
   Vector<ItemBehavior> m_chunkBehavior;
   Optional<PaintChunk::Id> m_currentChunkId;
   PaintChunkProperties m_currentProperties;
+  ItemBehavior m_nextDisplayItemBehavior;
 };
 
 #if DCHECK_IS_ON()
 class DisableNullPaintPropertyChecks {
   STACK_ALLOCATED();
   WTF_MAKE_NONCOPYABLE(DisableNullPaintPropertyChecks);
 
  public:
   DisableNullPaintPropertyChecks();
 
  private:
   AutoReset<bool> m_disabler;
 };
 #endif  // DCHECK_IS_ON()
 
 }  // namespace blink
 
 #endif  // PaintChunker_h