Slimming Paint phase 2 compositing algorithm plumbing & skeleton display list API.

Source/platform/graphics/ContentLayerDelegate.h

Index: Source/platform/graphics/ContentLayerDelegate.h
diff --git a/Source/platform/graphics/ContentLayerDelegate.h b/Source/platform/graphics/ContentLayerDelegate.h
index 968e1073a4b2a35498a253982561b5a7da1314f3..92279d803a42d1e53bf655d3e5ad3240a922ac85 100644
--- a/Source/platform/graphics/ContentLayerDelegate.h
+++ b/Source/platform/graphics/ContentLayerDelegate.h
@@ -36,6 +36,8 @@ class SkCanvas;
 namespace blink {
 
 class DisplayItemList;
+class DisplayItemTransformTree;
+class DisplayList;
 class GraphicsContext;
 class IntRect;
 
@@ -44,6 +46,9 @@ public:
     virtual void paint(GraphicsContext&, const IntRect& clip) = 0;
     virtual DisplayItemList* displayItemList() = 0;
 
+    virtual const DisplayList* displayList() const { return 0; }
+    virtual const DisplayItemTransformTree* transformTree() const { return 0; }
+
 protected:
     virtual ~GraphicsContextPainter() { }
 };
@@ -60,6 +65,11 @@ public:
     void paintContents(WebDisplayItemList*, const WebRect& clip, WebContentLayerClient::PaintingControlSetting = PaintDefaultBehavior) override;
     size_t approximateUnsharedMemoryUsage() const override;
 
+    const WebDisplayList* displayList() const override;
+
+    // This is only set on a root graphics layer. Alternatively, this could be set on the layer tree host.
+    const WebDisplayItemTransformTree* transformTree() const override;
+
 private:
     GraphicsContextPainter* m_painter;
 };