Make TreeScope::baseURL pure virtual

Source/core/dom/TreeScope.h

Index: Source/core/dom/TreeScope.h
diff --git a/Source/core/dom/TreeScope.h b/Source/core/dom/TreeScope.h
index cb444057b5c4e7b0317440ecf37f50355d241866..15e55ea9b6e57cec84f9711bfdb4de78df83ffd1 100644
--- a/Source/core/dom/TreeScope.h
+++ b/Source/core/dom/TreeScope.h
@@ -126,7 +126,7 @@ public:
 
     Element* getElementByAccessKey(const String& key) const;
 
-    const KURL& baseURL() const { return m_baseURL; }
+    virtual const KURL& baseURL() const = 0;
     KURL completeURL(const String&) const;
 
 protected:
@@ -142,8 +142,6 @@ protected:
 
     void setNeedsStyleRecalcForViewportUnits();
 
-    void setBaseURL(const KURL& baseURL) { m_baseURL = baseURL; }
-
 private:
     virtual void dispose() { }
 
@@ -170,8 +168,6 @@ private:
     OwnPtr<IdTargetObserverRegistry> m_idTargetObserverRegistry;
 
     mutable RefPtr<DOMSelection> m_selection;
-
-    KURL m_baseURL;
 };
 
 inline bool TreeScope::hasElementWithId(StringImpl* id) const