Add an about:flag to support alternative data saver features

chrome/browser/flag_descriptions.cc

Index: chrome/browser/flag_descriptions.cc
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index a05be8ee7f43a031a9f406ff54c3e219e09e8529..4a8a2846b98db506b4ed05944ff2f67f206d5889 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -1162,6 +1162,13 @@ const char kEnableDataReductionProxyLitePageDescription[] =
     "shown instead of image placeholders when Lo-Fi is on. Data Saver and "
     "Lo-Fi must be enabled for lite pages to be shown.";
 
+const char kEnableDataReductionProxyAlternativeBackEndName[] =
+    "Use an alternative Data Saver back end instead of the default one.";
+
+const char kEnableDataReductionProxyAlternativeBackEndDescription[] =
+    "Enable a different approach to saving data through an alternative back "
+    "end implementation";
+
 const char kDataReductionProxyCarrierTestName[] =
     "Enable a carrier-specific Data Reduction Proxy for testing.";