[ServivceWorker] Treat rejecting respondWith as a Network Error

Source/modules/serviceworkers/RespondWithObserver.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef RespondWithObserver_h
 #define RespondWithObserver_h
 
 #include "core/dom/ContextLifecycleObserver.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Forward.h"
@@ skipping 24 matching lines @@
     void responseWasRejected();
     void responseWasFulfilled(const ScriptValue&);
 
     void trace(Visitor*) { }
 
 private:
     class ThenFunction;
 
     RespondWithObserver(ExecutionContext*, int eventID);
 
-    // Sends a response back to the client. The null response means to fallback
-    // to native.
-    void sendResponse(Response*);
-
     int m_eventID;
 
     enum State { Initial, Pending, Done };
     State m_state;
 };
 
 } // namespace blink
 
 #endif // RespondWithObserver_h