Add toHTMLHeadElement(), and use it.

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 318ced439f0281f06f6538befdd02dd98b357892..c5187398aa2600e8ddce84b3bcb441ef47c7ab85 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -2296,10 +2296,10 @@ HTMLHeadElement* Document::head()
     if (!de)
         return 0;
 
-    for (Node* e = de->firstChild(); e; e = e->nextSibling())
-        if (e->hasTagName(headTag))
-            return static_cast<HTMLHeadElement*>(e);
-
+    for (Node* node = de->firstChild(); node; node = node->nextSibling()) {
+        if (node->hasTagName(headTag))
+            return toHTMLHeadElement(node);
+    }
     return 0;
 }