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

Source/core/editing/MoveSelectionCommand.cpp

Index: Source/core/editing/MoveSelectionCommand.cpp
diff --git a/Source/core/editing/MoveSelectionCommand.cpp b/Source/core/editing/MoveSelectionCommand.cpp
index 4fad6f0c039a3c0236ec693636c4da62e355f5b5..d4216e750c6be50542020853342fe7f962b3446e 100644
--- a/Source/core/editing/MoveSelectionCommand.cpp
+++ b/Source/core/editing/MoveSelectionCommand.cpp
@@ -32,7 +32,7 @@
 namespace WebCore {
 
 MoveSelectionCommand::MoveSelectionCommand(PassRefPtr<DocumentFragment> fragment, const Position& position, bool smartInsert, bool smartDelete)
-    : CompositeEditCommand(position.anchorNode()->document()), m_fragment(fragment), m_position(position), m_smartInsert(smartInsert), m_smartDelete(smartDelete)
+    : CompositeEditCommand(&position.anchorNode()->document()), m_fragment(fragment), m_position(position), m_smartInsert(smartInsert), m_smartDelete(smartDelete)
 {
     ASSERT(m_fragment);
 }