IDL: make optional arguments (without default) explicit sometimes

Source/modules/serviceworkers/Headers.h

Index: Source/modules/serviceworkers/Headers.h
diff --git a/Source/modules/serviceworkers/Headers.h b/Source/modules/serviceworkers/Headers.h
index 98732fa7aadc99bd05c74a7c1cd1276e4d041360..ac3baacb881ea4a2efbf474402cd08d867793dfb 100644
--- a/Source/modules/serviceworkers/Headers.h
+++ b/Source/modules/serviceworkers/Headers.h
@@ -5,6 +5,7 @@
 #ifndef Headers_h
 #define Headers_h
 
+#include "bindings/core/v8/Optional.h"
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "modules/serviceworkers/FetchHeaderList.h"
 #include "wtf/Forward.h"
@@ -42,8 +43,7 @@ public:
     bool has(const String& key, ExceptionState&);
     void set(const String& key, const String& value, ExceptionState&);
     unsigned long size() const;
-    void forEach(PassOwnPtr<HeadersForEachCallback>, ScriptValue&);
-    void forEach(PassOwnPtr<HeadersForEachCallback>);
+    void forEach(PassOwnPtr<HeadersForEachCallback>, const Optional<ScriptValue>&);
 
     void setGuard(Guard guard) { m_guard = guard; }
     Guard guard() const { return m_guard; }
@@ -58,7 +58,6 @@ private:
     Headers();
     // Shares the FetchHeaderList. Called when creating a Request or Response.
     explicit Headers(FetchHeaderList*);
-    void forEachInternal(PassOwnPtr<HeadersForEachCallback>, ScriptValue*);
 
     RefPtrWillBeMember<FetchHeaderList> m_headerList;
     Guard m_guard;