Revert of [Blob] BlobReader class & tests, and removal of all redundant reading.

net/base/upload_element_reader.cc

 // Copyright (c) 2012 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.
 
 #include "net/base/upload_element_reader.h"
 
 namespace net {
 
+const UploadDiskCacheEntryElementReader*
+UploadElementReader::AsDiskCacheEntryReaderForTests() const {
+  return nullptr;
+}
+
 const UploadBytesElementReader* UploadElementReader::AsBytesReader() const {
   return nullptr;
 }
 
 const UploadFileElementReader* UploadElementReader::AsFileReader() const {
   return nullptr;
 }
 
 bool UploadElementReader::IsInMemory() const {
   return false;
 }
 
 }  // namespace net