Have Node::document() return a reference instead of a pointer

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 b98c2293d4deda709c051cd12fb0ff314da2b244..0eab50c0c571f3fb6f3bbf1ac3fe061397827774 100644
--- a/Source/core/rendering/RenderFullScreen.cpp
+++ b/Source/core/rendering/RenderFullScreen.cpp
@@ -35,7 +35,7 @@ public:
         : RenderBlock(0)
         , m_owner(owner)
     {
-        setDocumentForAnonymous(owner->document());
+        setDocumentForAnonymous(&owner->document());
     }
 private:
     virtual bool isRenderFullScreenPlaceholder() const { return true; }
@@ -74,11 +74,9 @@ void RenderFullScreen::willBeDestroyed()
 
     // RenderObjects are unretained, so notify the document (which holds a pointer to a RenderFullScreen)
     // if it's RenderFullScreen is destroyed.
-    if (document()) {
-        FullscreenElementStack* controller = FullscreenElementStack::from(document());
-        if (controller->fullScreenRenderer() == this)
-            controller->fullScreenRendererDestroyed();
-    }
+    FullscreenElementStack* controller = FullscreenElementStack::from(&document());
+    if (controller->fullScreenRenderer() == this)
+        controller->fullScreenRendererDestroyed();
 
     RenderFlexibleBox::willBeDestroyed();
 }
@@ -162,7 +160,7 @@ void RenderFullScreen::unwrapRenderer()
     if (placeholder())
         placeholder()->remove();
     remove();
-    FullscreenElementStack::from(document())->setFullScreenRenderer(0);
+    FullscreenElementStack::from(&document())->setFullScreenRenderer(0);
 }
 
 void RenderFullScreen::setPlaceholder(RenderBlock* placeholder)