Use AtomicString type more consistently for mimeType / encoding

Source/core/loader/DocumentWriter.h

 /*
  * Copyright (C) 2010. Adam Barth. 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
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 27 matching lines @@
 class Document;
 class DocumentParser;
 class Frame;
 class KURL;
 class SecurityOrigin;
 class TextResourceDecoder;
 
 class DocumentWriter : public RefCounted<DocumentWriter> {
     WTF_MAKE_NONCOPYABLE(DocumentWriter);
 public:
-    static PassRefPtr<DocumentWriter> create(Document*, const String& mimeType = "", const String& encoding = "", bool encodingUserChoosen = false);
+    static PassRefPtr<DocumentWriter> create(Document*, const AtomicString& mimeType = emptyAtom, const AtomicString& encoding = emptyAtom, bool encodingUserChoosen = false);
 
     ~DocumentWriter();
 
     void end();
 
     // This is only called by ScriptController::executeScriptIfJavaScriptURL
     // and always contains the result of evaluating a javascript: url.
     void replaceDocument(const String&, Document* ownerDocument);
 
     void addData(const char* bytes, size_t length);
 
-    const String& mimeType() const { return m_decoderBuilder.mimeType(); }
-    const String& encoding() const { return m_decoderBuilder.encoding(); }
+    const AtomicString& mimeType() const { return m_decoderBuilder.mimeType(); }
+    const AtomicString& encoding() const { return m_decoderBuilder.encoding(); }
     bool encodingWasChosenByUser() const { return m_decoderBuilder.encodingWasChosenByUser(); }
 
     // Exposed for DocumentLoader::replaceDocument.
     void appendReplacingData(const String&);
 
     void setUserChosenEncoding(const String& charset);
 
     void setDocumentWasLoadedAsPartOfNavigation();
 
 private:
-    DocumentWriter(Document*, const String& mimeType, const String& encoding, bool encodingUserChoosen);
+    DocumentWriter(Document*, const AtomicString& mimeType, const AtomicString& encoding, bool encodingUserChoosen);
 
     PassRefPtr<Document> createDocument(const KURL&);
 
     Document* m_document;
     TextResourceDecoderBuilder m_decoderBuilder;
 
     RefPtr<DocumentParser> m_parser;
 };
 
 } // namespace WebCore
 
 #endif // DocumentWriter_h