cc: Make DisplayItemList::Append replay into an SkPicture

cc/trees/layer_tree_host_unittest.cc

Index: cc/trees/layer_tree_host_unittest.cc
diff --git a/cc/trees/layer_tree_host_unittest.cc b/cc/trees/layer_tree_host_unittest.cc
index 51994c74db535963f23bea466da78a6369c85e07..0b6467c410a6831a85fe735a079c2d998a54d4cf 100644
--- a/cc/trees/layer_tree_host_unittest.cc
+++ b/cc/trees/layer_tree_host_unittest.cc
@@ -1325,11 +1325,11 @@ class TestOpacityChangeLayerDelegate : public ContentLayerClient {
     if (test_layer_)
       test_layer_->SetOpacity(0.f);
   }
-  scoped_refptr<DisplayItemList> PaintContentsToDisplayList(
+  void PaintContentsToDisplayList(
+      DisplayItemList* display_list,
       const gfx::Rect& clip,
       PaintingControlSetting picture_control) override {
     NOTIMPLEMENTED();
-    return DisplayItemList::Create();
   }
   bool FillsBoundsCompletely() const override { return false; }
 
@@ -2790,11 +2790,11 @@ class LayerTreeHostTestChangeLayerPropertiesInPaintContents
       layer_->SetBounds(gfx::Size(2, 2));
     }
 
-    scoped_refptr<DisplayItemList> PaintContentsToDisplayList(
+    void PaintContentsToDisplayList(
+        DisplayItemList* display_list,
         const gfx::Rect& clip,
         PaintingControlSetting picture_control) override {
       NOTIMPLEMENTED();
-      return DisplayItemList::Create();
     }
 
     bool FillsBoundsCompletely() const override { return false; }