Remove willRequestResource callback, it is unused outside of tests.

Source/core/loader/FrameFetchContext.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 63 matching lines @@
     void dispatchWillSendRequest(unsigned long identifier, ResourceRequest&, const ResourceResponse& redirectResponse, const FetchInitiatorInfo& = FetchInitiatorInfo()) override;
     void dispatchDidLoadResourceFromMemoryCache(const ResourceRequest&, const ResourceResponse&) override;
     void dispatchDidReceiveResponse(unsigned long identifier, const ResourceResponse&, ResourceLoader* = 0) override;
     void dispatchDidReceiveData(unsigned long identifier, const char* data, int dataLength, int encodedDataLength) override;
     void dispatchDidDownloadData(unsigned long identifier, int dataLength, int encodedDataLength)  override;
     void dispatchDidFinishLoading(unsigned long identifier, double finishTime, int64_t encodedDataLength) override;
     void dispatchDidFail(unsigned long identifier, const ResourceError&, bool isInternalRequest) override;
     void sendRemainingDelegateMessages(unsigned long identifier, const ResourceResponse&, int dataLength) override;
 
     bool shouldLoadNewResource(Resource::Type) const override;
-    void dispatchWillRequestResource(FetchRequest*) override;
     void willStartLoadingResource(ResourceRequest&) override;
     void didLoadResource() override;
 
     void addResourceTiming(const ResourceTimingInfo&) override;
     bool allowImage(bool imagesEnabled, const KURL&) const override;
     bool canRequest(Resource::Type, const ResourceRequest&, const KURL&, const ResourceLoaderOptions&, bool forPreload, FetchRequest::OriginRestriction) const override;
 
     bool isControlledByServiceWorker() const override;
     int64_t serviceWorkerID() const override;
 
@@ skipping 31 matching lines @@
     // FIXME: Oilpan: Ideally this should just be a traced Member but that will
     // currently leak because ComputedStyle and its data are not on the heap.
     // See crbug.com/383860 for details.
     RawPtrWillBeWeakMember<Document> m_document;
     RawPtrWillBeMember<DocumentLoader> m_documentLoader;
 };
 
 }
 
 #endif