Adds feature flag for chrome-proxy-ect header (default off)

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 b36fd93d5ee321020b87c31dd20c128ac4ca1e5c..7ac7108d46f5b533b6c3f9cd614d3e62311675f9 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
@@ -19,6 +19,7 @@
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.h"
 #include "components/data_reduction_proxy/core/browser/data_use_group.h"
 #include "components/data_reduction_proxy/core/browser/data_use_group_provider.h"
+#include "components/data_reduction_proxy/core/common/data_reduction_proxy_features.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_params.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_util.h"
@@ -122,7 +123,9 @@ void VerifyHttpRequestHeaders(bool via_chrome_proxy,
                               const net::HttpRequestHeaders& headers) {
   if (via_chrome_proxy) {
     DCHECK(headers.HasHeader(chrome_proxy_header()));
-    DCHECK(headers.HasHeader(chrome_proxy_ect_header()));
+    DCHECK_EQ(
+        data_reduction_proxy::features::IsDataReductionProxyECTHeaderEnabled(),
+        headers.HasHeader(chrome_proxy_ect_header()));
   } else {
     DCHECK(!headers.HasHeader(chrome_proxy_header()));
     DCHECK(!headers.HasHeader(chrome_proxy_accept_transform_header()));
@@ -526,6 +529,9 @@ void DataReductionProxyNetworkDelegate::MaybeAddChromeProxyECTHeader(
     const net::URLRequest& request) const {
   DCHECK(thread_checker_.CalledOnValidThread());
 
+  if (!data_reduction_proxy::features::IsDataReductionProxyECTHeaderEnabled())
+    return;
+
   // This method should be called only when the resolved proxy was a data
   // saver proxy.
   DCHECK(request.url().is_valid());
@@ -562,6 +568,9 @@ void DataReductionProxyNetworkDelegate::RemoveChromeProxyECTHeader(
     net::HttpRequestHeaders* request_headers) const {
   DCHECK(thread_checker_.CalledOnValidThread());
 
+  if (!data_reduction_proxy::features::IsDataReductionProxyECTHeaderEnabled())
+    return;
+
   request_headers->RemoveHeader(chrome_proxy_ect_header());
 }