ServiceWorker: Fix conversion from Request headers to WebServiceWorkerRequest headers

public/platform/WebServiceWorkerRequest.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 WebServiceWorkerRequest_h
 #define WebServiceWorkerRequest_h
 
 #include "WebCommon.h"
 #include "public/platform/WebPrivatePtr.h"
 #include "public/platform/WebReferrerPolicy.h"
@@ skipping 29 matching lines @@
     void reset();
     void assign(const WebServiceWorkerRequest&);
 
     void setURL(const WebURL&);
     WebURL url() const;
 
     void setMethod(const WebString&);
     WebString method() const;
 
     void setHeader(const WebString& key, const WebString& value);
+
+    // If the key already exists, the value is appended to the existing value
+    // with a comma delimiter between them.
+    void appendHeader(const WebString& key, const WebString& value);
+
     void visitHTTPHeaderFields(WebHTTPHeaderVisitor*) const;
 
     void setBlob(const WebString& uuid, long long size);
 
     void setReferrer(const WebString&, WebReferrerPolicy);
     WebURL referrerUrl() const;
     WebReferrerPolicy referrerPolicy() const;
 
     void setIsReload(bool);
     bool isReload() const;
 
 #if INSIDE_BLINK
     const HTTPHeaderMap& headers() const;
     PassRefPtr<BlobDataHandle> blobDataHandle() const;
     const Referrer& referrer() const;
 #endif
 
 private:
     WebPrivatePtr<WebServiceWorkerRequestPrivate> m_private;
 };
 
 } // namespace blink
 
 #endif // WebServiceWorkerRequest_h