[ServiceWorker] Make Request class better conformance with the spec.

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 38f82701dc665f5d1c8299571ea4688095fdf409..140380f1f4dca4545069e03994e693e2d75df8f9 100644
--- a/Source/modules/serviceworkers/Headers.h
+++ b/Source/modules/serviceworkers/Headers.h
@@ -47,15 +47,16 @@ public:
     void setGuard(Guard guard) { m_guard = guard; }
     Guard guard() const { return m_guard; }
 
+    // The header list in |m_headerList| must be cleared before calling these methods.
+    void fillWith(const Headers*, ExceptionState&);
+    void fillWith(const Dictionary&, ExceptionState&);
+
 private:
     Headers();
     // Shares the FetchHeaderList. Called when creating a Request or Response.
     explicit Headers(FetchHeaderList*);
     void forEachInternal(PassOwnPtr<HeadersForEachCallback>, ScriptValue*);
 
-    void fillWith(const Headers*, ExceptionState&);
-    void fillWith(const Dictionary&, ExceptionState&);
-
     RefPtr<FetchHeaderList> m_headerList;
     Guard m_guard;
 };