Move visual rect unioning between paired items to cc::DisplayItemList.

cc/trees/layer_tree_host_pixeltest_tiles.cc

Index: cc/trees/layer_tree_host_pixeltest_tiles.cc
diff --git a/cc/trees/layer_tree_host_pixeltest_tiles.cc b/cc/trees/layer_tree_host_pixeltest_tiles.cc
index a7833ddd0879db5707da7b53bd9ee7f80ef84cd1..b6b1bb4d44872f5bab8c0bbf33b774f6e41c4c2a 100644
--- a/cc/trees/layer_tree_host_pixeltest_tiles.cc
+++ b/cc/trees/layer_tree_host_pixeltest_tiles.cc
@@ -132,7 +132,7 @@ class BlueYellowClient : public ContentLayerClient {
     paint.setColor(SK_ColorYELLOW);
     canvas->drawRect(gfx::RectToSkRect(yellow_rect), paint);
 
-    display_list->CreateAndAppendItem<DrawingDisplayItem>(
+    display_list->CreateAndAppendDrawingItem<DrawingDisplayItem>(
         PaintableRegion(), recorder.finishRecordingAsPicture());
     display_list->Finalize();
     return display_list;