Remove useless null checks from Node::document() call sites

Source/core/dom/EventPathWalker.cpp

Index: Source/core/dom/EventPathWalker.cpp
diff --git a/Source/core/dom/EventPathWalker.cpp b/Source/core/dom/EventPathWalker.cpp
index de1d4d01b3fe26af72df40aa49a370c36560463c..15b35ce713906c2668615dd50cedbcbf8b6ae3d5 100644
--- a/Source/core/dom/EventPathWalker.cpp
+++ b/Source/core/dom/EventPathWalker.cpp
@@ -39,11 +39,7 @@ EventPathWalker::EventPathWalker(const Node* node)
     , m_isVisitingInsertionPointInReprojection(false)
 {
     ASSERT(node);
-    // FIXME: It's not clear if we need this document check, but I think we do
-    // since DocType nodes from document.implementation.createDocumentType
-    // don't have a document().
-    if (Document* document = node->document())
-        document->updateDistributionForNodeIfNeeded(const_cast<Node*>(node));
+    node->document()->updateDistributionForNodeIfNeeded(const_cast<Node*>(node));
 }
 
 Node* EventPathWalker::parent(const Node* node)