Add an about:flag to support alternative data saver features

components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc
index 470a67597e5b5c075b4e4a3cbdfcbc1826ad0979..1271e4e66fa616ed9ab9fd0053c3c634f45f36db 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_request_options.cc
@@ -17,6 +17,7 @@
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_config.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_switches.h"
@@ -106,6 +107,7 @@ void DataReductionProxyRequestOptions::UpdateExperiments() {
       base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
           data_reduction_proxy::switches::kDataReductionProxyExperiment);
 
+  // The command line override takes precedence over other "exp" directives.
   if (!experiments.empty()) {
     base::StringTokenizer experiment_tokenizer(experiments, ", ");
     experiment_tokenizer.set_quote_chars("\"");
@@ -113,7 +115,14 @@ void DataReductionProxyRequestOptions::UpdateExperiments() {
       if (!experiment_tokenizer.token().empty())
         experiments_.push_back(experiment_tokenizer.token());
     }
+  } else if (base::FeatureList::IsEnabled(
+                 features::kDataReductionProxyAlternativeBackEnd)) {
+    experiments_.push_back(chrome_proxy_alternative_back_end());
+  } else if (params::AreLitePagesEnabledViaFlags()) {
+    experiments_.push_back(chrome_proxy_lite_page_ignore_blacklist());
   } else {
+    // If no other "exp" directive is forced by flags, add the field trial
+    // value.
     AddServerExperimentFromFieldTrial();
   }