Oilpan: Prepare to move RenderObject and RenderObjectChildList to Oilpan heap.

Source/core/rendering/RenderFullScreen.cpp

Index: Source/core/rendering/RenderFullScreen.cpp
diff --git a/Source/core/rendering/RenderFullScreen.cpp b/Source/core/rendering/RenderFullScreen.cpp
index 86230a322c9e4c8e30366b6a952723fa386059d9..41c5ecee62bf56091de536791ade26b2e94fa812 100644
--- a/Source/core/rendering/RenderFullScreen.cpp
+++ b/Source/core/rendering/RenderFullScreen.cpp
@@ -52,7 +52,7 @@ void RenderFullScreenPlaceholder::willBeDestroyed()
 
 RenderFullScreen::RenderFullScreen()
     : RenderFlexibleBox(0)
-    , m_placeholder(0)
+    , m_placeholder(nullptr)
 {
     setReplaced(false);
 }
@@ -64,6 +64,12 @@ RenderFullScreen* RenderFullScreen::createAnonymous(Document* document)
     return renderer;
 }
 
+void RenderFullScreen::trace(Visitor* visitor)
+{
+    visitor->trace(m_placeholder);
+    RenderFlexibleBox::trace(visitor);
+}
+
 void RenderFullScreen::willBeDestroyed()
 {
     if (m_placeholder) {