Revert of Cleanup DataReductionProxy (DRP) Brotli code

components/data_reduction_proxy/core/browser/data_reduction_proxy_network_delegate.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_network_delegate.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_network_delegate.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_network_delegate.cc
index 0a37807e2bb03372e4b2ba1aa9ffa91f3bc69dac..74d7e3abeb480d0eb2537b9251729370b2dc1026 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_network_delegate.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_network_delegate.cc
@@ -181,7 +181,8 @@
       data_reduction_proxy_bypass_stats_(nullptr),
       data_reduction_proxy_request_options_(request_options),
       data_reduction_proxy_io_data_(nullptr),
-      configurator_(configurator) {
+      configurator_(configurator),
+      exclude_chrome_proxy_header_for_testing_(false) {
   DCHECK(data_reduction_proxy_config_);
   DCHECK(data_reduction_proxy_request_options_);
   DCHECK(configurator_);
@@ -325,7 +326,8 @@
   }
   MaybeAddBrotliToAcceptEncodingHeader(proxy_info, headers, *request);
 
-  data_reduction_proxy_request_options_->AddRequestHeader(headers);
+  if (!exclude_chrome_proxy_header_for_testing_)
+    data_reduction_proxy_request_options_->AddRequestHeader(headers);
   if (lofi_decider)
     lofi_decider->MaybeSetIgnorePreviewsBlacklistDirective(headers);
 }