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

Source/core/dom/EventPathWalker.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 21 matching lines @@
 #include "core/dom/shadow/ShadowRoot.h"
 
 namespace WebCore {
 
 EventPathWalker::EventPathWalker(const Node* node)
     : m_node(node)
     , m_distributedNode(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)
 {
     EventPathWalker walker(node);
     walker.moveToParent();
     return walker.node();
 }
 
 void EventPathWalker::moveToParent()
@@ skipping 20 matching lines @@
         m_node = insertionPoint;
         m_isVisitingInsertionPointInReprojection = true;
         return;
     }
     m_node = shadowRoot->host();
     m_distributedNode = m_node;
     m_isVisitingInsertionPointInReprojection = false;
 }
 
 } // namespace