Refactor the way PaintArtifactCompositor is attached and used.

third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h

Index: third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
diff --git a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
index c74fa8699455621ffcd5e6db11ca38e78c3f8040..34b6e2f9f104ae073f907d5b8bce778bf9b087af 100644
--- a/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
+++ b/third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.h
@@ -8,6 +8,7 @@
 #include "base/memory/ref_counted.h"
 #include "platform/PlatformExport.h"
 #include "wtf/Noncopyable.h"
+#include "wtf/PtrUtil.h"
 #include "wtf/Vector.h"
 #include <memory>
 
@@ -36,9 +37,13 @@ struct PaintChunk;
 class PLATFORM_EXPORT PaintArtifactCompositor {
     WTF_MAKE_NONCOPYABLE(PaintArtifactCompositor);
 public:
-    PaintArtifactCompositor();
     ~PaintArtifactCompositor();
 
+    static std::unique_ptr<PaintArtifactCompositor> create()
+    {
+        return wrapUnique(new PaintArtifactCompositor());
+    }
+
     // Updates the layer tree to match the provided paint artifact.
     void update(const PaintArtifact&);
 
@@ -60,6 +65,8 @@ public:
     ExtraDataForTesting* getExtraDataForTesting() const { return m_extraDataForTesting.get(); }
 
 private:
+    PaintArtifactCompositor();
+
     class ContentLayerClientImpl;
 
     // Builds a leaf layer that represents a single paint chunk.
@@ -75,6 +82,7 @@ private:
 
     bool m_extraDataForTestingEnabled = false;
     std::unique_ptr<ExtraDataForTesting> m_extraDataForTesting;
+    friend class StubChromeClientForSPv2;
 };
 
 } // namespace blink