Use AtomicString type more consistently for mimeType / encoding

Source/core/loader/FrameLoader.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) Research In Motion Limited 2009. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
@@ skipping 68 matching lines @@
     ~FrameLoader();
 
     void init();
 
     Frame* frame() const { return m_frame; }
 
     MixedContentChecker* mixedContentChecker() const { return &m_mixedContentChecker; }
 
     // These functions start a load. All eventually call into loadWithNavigationAction() or loadInSameDocument().
     void load(const FrameLoadRequest&); // The entry point for non-reload, non-history loads.
-    void reload(ReloadPolicy = NormalReload, const KURL& overrideURL = KURL(), const String& overrideEncoding = String());
+    void reload(ReloadPolicy = NormalReload, const KURL& overrideURL = KURL(), const AtomicString& overrideEncoding = nullAtom);
     void loadHistoryItem(HistoryItem*, HistoryLoadType = HistoryDifferentDocumentLoad); // The entry point for all back/forward loads
 
     static void reportLocalLoadFailed(Frame*, const String& url);
 
     // FIXME: These are all functions which stop loads. We have too many.
     // Warning: stopAllLoaders can and will detach the Frame out from under you. All callers need to either protect the Frame
     // or guarantee they won't in any way access the Frame after stopAllLoaders returns.
     void stopAllLoaders();
     void stopLoading();
     bool closeURL();
@@ skipping 129 matching lines @@
 
     bool shouldPerformFragmentNavigation(bool isFormSubmission, const String& httpMethod, FrameLoadType, const KURL&);
     void scrollToFragmentWithParentBoundary(const KURL&);
 
     void checkLoadCompleteForThisFrame();
 
     void closeOldDataSources();
 
     // Calls continueLoadAfterNavigationPolicy
     void loadWithNavigationAction(const NavigationAction&, FrameLoadType, PassRefPtr<FormState>,
-        const SubstituteData&, ClientRedirectPolicy = NotClientRedirect, const String& overrideEncoding = String());
+        const SubstituteData&, ClientRedirectPolicy = NotClientRedirect, const AtomicString& overrideEncoding = nullAtom);
 
     void detachChildren();
     void closeAndRemoveChild(Frame*);
 
     enum HistoryItemPolicy {
         CreateNewHistoryItem,
         DoNotCreateNewHistoryItem
     };
     void setHistoryItemStateForCommit(HistoryItemPolicy);
 
@@ skipping 43 matching lines @@
 
     bool m_didAccessInitialDocument;
     Timer<FrameLoader> m_didAccessInitialDocumentTimer;
 
     SandboxFlags m_forcedSandboxFlags;
 };
 
 } // namespace WebCore
 
 #endif // FrameLoader_h