Make sure getAttribute() / setAttribute() callers use AtomicStrings

Source/core/dom/Document.h

Index: Source/core/dom/Document.h
diff --git a/Source/core/dom/Document.h b/Source/core/dom/Document.h
index cc3da6f92a991541715d2217d5a188243759a873..337397fba0dcdc434b3e431ba0f375e26932fa93 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -324,11 +324,11 @@ public:
 
     String defaultCharset() const;
 
-    String inputEncoding() const { return Document::encodingName(); }
-    String charset() const { return Document::encodingName(); }
-    String characterSet() const { return Document::encodingName(); }
+    AtomicString inputEncoding() const { return Document::encodingName(); }
+    AtomicString charset() const { return Document::encodingName(); }
+    AtomicString characterSet() const { return Document::encodingName(); }
 
-    String encodingName() const;
+    AtomicString encodingName() const;
 
     void setCharset(const String&);