[ServiceWorker] Make fetch() method better conformance with the spec.

Source/core/fetch/Resource.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 324 matching lines @@
         bool hasMaxAge = std::isfinite(response.cacheControlMaxAge());
         bool hasExpires = std::isfinite(response.expires());
         // TODO: consider catching Cache-Control "private" and "public" here.
         if (!hasMaxAge && !hasExpires)
             return false;
     }
 
     return currentAge(response, responseTimestamp) <= freshnessLifetime(response, responseTimestamp);
 }
 
-const ResourceRequest& Resource::lastResourceRequest()
+const ResourceRequest& Resource::lastResourceRequest() const
 {
     if (!m_redirectChain.size())
         return m_resourceRequest;
     return m_redirectChain.last().m_request;
 }
 
 void Resource::willSendRequest(ResourceRequest& request, const ResourceResponse& response)
 {
     m_redirectChain.append(RedirectPair(request, response));
     m_requestedFromNetworkingLayer = true;
@@ skipping 639 matching lines @@
         return "ImportResource";
     case Resource::Media:
         return "Media";
     }
     ASSERT_NOT_REACHED();
     return "Unknown";
 }
 #endif // !LOG_DISABLED
 
 }