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

Source/core/editing/markup.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009, 2010, 2011 Google Inc. All rights reserved.
  * Copyright (C) 2011 Igalia S.L.
  * Copyright (C) 2011 Motorola Mobility. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 884 matching lines @@
     }
 
     return fragment.release();
 }
 
 String createFullMarkup(const Node* node)
 {
     if (!node)
         return String();
 
-    Document* document = node->document();
-    if (!document)
-        return String();
-
-    Frame* frame = document->frame();
+    Frame* frame = node->document()->frame();
     if (!frame)
         return String();
 
     // FIXME: This is never "for interchange". Is that right?
     String markupString = createMarkup(node, IncludeNode, 0);
     Node::NodeType nodeType = node->nodeType();
     if (nodeType != Node::DOCUMENT_NODE && nodeType != Node::DOCUMENT_TYPE_NODE)
         markupString = frame->documentTypeString() + markupString;
 
     return markupString;
 }
 
 String createFullMarkup(const Range* range)
 {
     if (!range)
         return String();
 
     Node* node = range->startContainer();
     if (!node)
         return String();
 
-    Document* document = node->document();
-    if (!document)
-        return String();
-
-    Frame* frame = document->frame();
+    Frame* frame = node->document()->frame();
     if (!frame)
         return String();
 
     // FIXME: This is always "for interchange". Is that right? See the previous method.
     return frame->documentTypeString() + createMarkup(range, 0, AnnotateForInterchange);
 }
 
 String urlToMarkup(const KURL& url, const String& title)
 {
     StringBuilder markup;
@@ skipping 134 matching lines @@
     if (containerNode->hasOneChild()) {
         containerNode->replaceChild(textNode.release(), containerNode->firstChild(), es);
         return;
     }
 
     containerNode->removeChildren();
     containerNode->appendChild(textNode.release(), es);
 }
 
 }