Return chrome-proxy-ect header code (post M59 branch)

components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc

Index: components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc
diff --git a/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc b/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc
index 3a697aecaf897b97408cf67eec4fbecad88bc753..d8a021928967a12591b5460e750a99d0d08a8048 100644
--- a/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc
+++ b/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc
@@ -29,6 +29,7 @@ using base::TimeDelta;
 namespace {
 
 const char kChromeProxyHeader[] = "chrome-proxy";
+const char kChromeProxyECTHeader[] = "chrome-proxy-ect";
 const char kChromeProxyAcceptTransformHeader[] =
     "chrome-proxy-accept-transform";
 const char kChromeProxyContentTransformHeader[] =
@@ -126,6 +127,10 @@ const char* chrome_proxy_header() {
   return kChromeProxyHeader;
 }
 
+const char* chrome_proxy_ect_header() {
+  return kChromeProxyECTHeader;
+}
+
 const char* chrome_proxy_accept_transform_header() {
   return kChromeProxyAcceptTransformHeader;
 }