Mark DOMStringList.contains() as deprecated, add console warning.

Source/core/dom/DOMStringList.h

Index: Source/core/dom/DOMStringList.h
diff --git a/Source/core/dom/DOMStringList.h b/Source/core/dom/DOMStringList.h
index 1c94de5e38ee34b75088ff820fc28c04a6999b82..5131c51fb8ab21837b997e5f9ec2456d6db8346a 100644
--- a/Source/core/dom/DOMStringList.h
+++ b/Source/core/dom/DOMStringList.h
@@ -53,6 +53,7 @@ public:
 
     // Implements the IDL.
     size_t length() const { return m_strings.size(); }
+    String anonymousIndexedGetter(unsigned index) const { return item(index); }
     String item(unsigned index) const;
     bool contains(const String& str) const;