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

components/data_reduction_proxy/core/common/data_reduction_proxy_features.cc

Index: components/data_reduction_proxy/core/common/data_reduction_proxy_features.cc
diff --git a/components/data_reduction_proxy/core/common/data_reduction_proxy_features.cc b/components/data_reduction_proxy/core/common/data_reduction_proxy_features.cc
index 8e7e96ee4b7ffb96bb2de32924aa668ff6543615..9d385b7f23a4b8d7e5b822be406a6c4640771a53 100644
--- a/components/data_reduction_proxy/core/common/data_reduction_proxy_features.cc
+++ b/components/data_reduction_proxy/core/common/data_reduction_proxy_features.cc
@@ -12,5 +12,14 @@ namespace features {
 const base::Feature kDataReductionMainMenu{"DataReductionProxyMainMenu",
                                            base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enables sending the Effective Connection Type header to the Data Reduction
+// Proxy.
+const base::Feature kDataReductionProxyECTHeader{
+    "DataReductionProxyECTHeader", base::FEATURE_DISABLED_BY_DEFAULT};
+
+bool IsDataReductionProxyECTHeaderEnabled() {
+  return base::FeatureList::IsEnabled(kDataReductionProxyECTHeader);
+}
+
 }  // namespace features
 }  // namespace data_reduction_proxy