New CPAT support in DataReductionProxyConfig guarded by feature flag.

components/data_reduction_proxy/core/common/data_reduction_proxy_features.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_features.h"
 
 namespace data_reduction_proxy {
 namespace features {
 
 // Enables the Data Reduction Proxy footer in the main menu on Android.
 const base::Feature kDataReductionMainMenu{"DataReductionProxyMainMenu",
                                            base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables the site breakdown on the Data Reduction Proxy settings page.
 const base::Feature kDataReductionSiteBreakdown{
     "DataReductionProxySiteBreakdown", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enables letting proxy server decide on transformations vs. client

[bengr, 2017/05/23 17:51:25]

Please rewrite to make this clearer:

// Enables a new version of the data reduction proxy protocol where the server
// decides if a server-generated preview should be served. The previous
// version required the client to make this decision. The new protocol relies
// on updates primarily to the Chrome-Proxy-Accept-Transform header.

[dougarnett, 2017/05/23 18:27:44]

Done.

+// deciding locally by effective connection type. Intended to be used to
+// enable newer CPAT protocol to the proxy server.
+const base::Feature kDataReductionProxyDecidesTransform{
+    "DataReductionProxyDecidesTransform", base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace features
 }  // namespace data_reduction_proxy