IDL: make optional arguments (without default) explicit sometimes

Source/core/css/FontFaceSet.h

Index: Source/core/css/FontFaceSet.h
diff --git a/Source/core/css/FontFaceSet.h b/Source/core/css/FontFaceSet.h
index 19a01bcc8eaf316131e723188d98bbc7d06c0fa9..5d575eb2aa8dc2cb349d6d84e6a421c4349eeec2 100644
--- a/Source/core/css/FontFaceSet.h
+++ b/Source/core/css/FontFaceSet.h
@@ -26,6 +26,7 @@
 #ifndef FontFaceSet_h
 #define FontFaceSet_h
 
+#include "bindings/core/v8/Optional.h"
 #include "bindings/core/v8/ScriptPromise.h"
 #include "core/css/FontFace.h"
 #include "core/css/FontFaceSetForEachCallback.h"
@@ -80,8 +81,7 @@ public:
     void add(FontFace*, ExceptionState&);
     void clear();
     bool remove(FontFace*, ExceptionState&);
-    void forEach(PassOwnPtr<FontFaceSetForEachCallback>, ScriptValue& thisArg) const;
-    void forEach(PassOwnPtr<FontFaceSetForEachCallback>) const;
+    void forEach(PassOwnPtr<FontFaceSetForEachCallback>, const Optional<ScriptValue>& thisArg) const;
     bool has(FontFace*, ExceptionState&) const;
 
     unsigned long size() const;
@@ -136,7 +136,6 @@ private:
     bool hasLoadedFonts() const { return !m_loadedFonts.isEmpty() || !m_failedFonts.isEmpty(); }
 
     bool inActiveDocumentContext() const;
-    void forEachInternal(PassOwnPtr<FontFaceSetForEachCallback>, ScriptValue* thisArg) const;
     void addToLoadingFonts(PassRefPtrWillBeRawPtr<FontFace>);
     void removeFromLoadingFonts(PassRefPtrWillBeRawPtr<FontFace>);
     void fireLoadingEvent();