Implement lazy block layout prototype behind a runtime flag.

Source/core/rendering/RenderObject.cpp

Index: Source/core/rendering/RenderObject.cpp
diff --git a/Source/core/rendering/RenderObject.cpp b/Source/core/rendering/RenderObject.cpp
index ca9f76eba37ddcfedea03ab2509ee7dce565ec96..3b587c94e9923419b5738873a7c8391818a26e55 100644
--- a/Source/core/rendering/RenderObject.cpp
+++ b/Source/core/rendering/RenderObject.cpp
@@ -62,6 +62,7 @@
 #include "core/rendering/RenderLayer.h"
 #include "core/rendering/RenderLayerBacking.h"
 #include "core/rendering/RenderLayerCompositor.h"
+#include "core/rendering/RenderLazyBlock.h"
 #include "core/rendering/RenderListItem.h"
 #include "core/rendering/RenderMultiColumnBlock.h"
 #include "core/rendering/RenderNamedFlowThread.h"
@@ -209,6 +210,8 @@ RenderObject* RenderObject::createObject(Element* element, RenderStyle* style)
     case GRID:
     case INLINE_GRID:
         return new (arena) RenderGrid(element);
+    case LAZY_BLOCK:
+        return new (arena) RenderLazyBlock(element);
     }
 
     return 0;