Reuse cc::PictureLayers when possible for SPv2.

third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.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 PaintArtifactCompositor_h
 #define PaintArtifactCompositor_h
 
 #include "base/memory/ref_counted.h"
 #include "platform/PlatformExport.h"
 #include "wtf/Noncopyable.h"
@@ skipping 58 matching lines @@
 
     class ContentLayerClientImpl;
 
     // Builds a leaf layer that represents a single paint chunk.
     // Note: cc::Layer API assumes the layer bounds to start at (0, 0) but the bounding box of
     // a paint chunk does not necessarily start at (0, 0) and could even be negative. Internally
     // the generated layer translates the paint chunk to align the bounding box to (0, 0) and
     // return the actual origin of the paint chunk in output parameter layerOffset.
     scoped_refptr<cc::Layer> layerForPaintChunk(const PaintArtifact&, const PaintChunk&, gfx::Vector2dF& layerOffset);
 
+    // Finds a client among the current vector of clients that matches the paint chunk's id,
+    // or otherwise allocates a new one.
+    std::unique_ptr<ContentLayerClientImpl> clientForPaintChunk(const PaintChunk&);
+
     scoped_refptr<cc::Layer> m_rootLayer;
     std::unique_ptr<WebLayer> m_webLayer;
-    Vector<std::unique_ptr<ContentLayerClientImpl>> m_contentLayerClients;
+    Vector<std::unique_ptr<ContentLayerClientImpl>> m_currentContentLayerClients;
+    Vector<std::unique_ptr<ContentLayerClientImpl>> m_newContentLayerClients;
 
     bool m_extraDataForTestingEnabled = false;
     std::unique_ptr<ExtraDataForTesting> m_extraDataForTesting;
     friend class StubChromeClientForSPv2;
 };
 
 } // namespace blink
 
 #endif // PaintArtifactCompositor_h