Add an about:flag to support alternative data saver features

components/data_reduction_proxy/core/browser/data_reduction_proxy_network_delegate_unittest.cc

 // 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.
 
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_network_delegate.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <map>
@@ skipping 176 matching lines @@
     return false;
   }
 
   void RemoveAcceptTransformHeader(
       net::HttpRequestHeaders* headers) const override {
     if (ignore_is_using_data_reduction_proxy_check_)
       return;
     headers->RemoveHeader(chrome_proxy_accept_transform_header());
   }
 
-  void MaybeSetIgnorePreviewsBlacklistDirective(
-      net::HttpRequestHeaders* headers) const override {}
-
   bool ShouldRecordLoFiUMA(const net::URLRequest& request) const override {
     return should_request_lofi_resource_;
   }
 
   bool IsClientLoFiImageRequest(const net::URLRequest& request) const override {
     return should_be_client_lofi_;
   }
 
   bool IsClientLoFiAutoReloadRequest(
       const net::URLRequest& request) const override {
@@ skipping 1662 matching lines @@
   EXPECT_EQ(static_cast<int64_t>(net::HttpUtil::AssembleRawHeaders(
                                      kHeaders, sizeof(kHeaders) - 1)
                                      .size() +
                                  10000 - request->GetTotalReceivedBytes()),
             GetSavings());
 }
 
 }  // namespace
 
 }  // namespace data_reduction_proxy