Add an about:flag to support alternative data saver features

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 19a4740c5957634ca099e9a71223a39f073889dc..b6d3075f4b431b4a3a289cbbbd3b7c23c30bd74b 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1892,6 +1892,12 @@ const FeatureEntry kFeatureEntries[] = {
      flag_descriptions::kEnableDataReductionProxyLitePageDescription, kOsAll,
      SINGLE_VALUE_TYPE(
          data_reduction_proxy::switches::kEnableDataReductionProxyLitePage)},
+    {"enable-data-reduction-proxy-alternative-back-end",

[tbansal1, 2017/05/19 16:27:23]

I still think this should be a dropdown flag (with two options: Default and
Alternative). The flag should map to the existing switch for setting the server
experiments.

Right now, we have two different switches which do exactly the same thing.
Having a single switch would reduce the confusion. Also, see:
https://bugs.chromium.org/p/chromium/issues/detail?id=656195#c1

[RyanSturm, 2017/05/23 22:04:57]

Done.

+     flag_descriptions::kEnableDataReductionProxyAlternativeBackEndName,
+     flag_descriptions::kEnableDataReductionProxyAlternativeBackEndDescription,
+     kOsAll,
+     FEATURE_VALUE_TYPE(data_reduction_proxy::features::
+                            kDataReductionProxyAlternativeBackEnd)},
 #if defined(OS_ANDROID)
     {"enable-data-reduction-proxy-savings-promo",
      flag_descriptions::kEnableDataReductionProxySavingsPromoName,