Add "q=preview" directive on main frame requests on poor networks

components/data_reduction_proxy/content/browser/content_lofi_decider.cc

 // Copyright 2015 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/content/browser/content_lofi_decider.h"
 
 #include <string>
 
 #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 "content/public/browser/resource_request_info.h"
+#include "net/base/load_flags.h"
 #include "net/http/http_request_headers.h"
 
 namespace data_reduction_proxy {
 
 ContentLoFiDecider::ContentLoFiDecider() {}
 
 ContentLoFiDecider::~ContentLoFiDecider() {}
 
 bool ContentLoFiDecider::IsUsingLoFiMode(const net::URLRequest& request) const {
   const content::ResourceRequestInfo* request_info =
@@ skipping 18 matching lines @@
 
   if (!request_info)
     return false;
 
   // The Lo-Fi directive should not be added for users in the Lo-Fi field
   // trial "Control" group. Check that the user is in a group that should
   // get "q=low".
   bool lofi_enabled_via_flag_or_field_trial =
       params::IsLoFiOnViaFlags() || params::IsIncludedInLoFiEnabledFieldTrial();
 
+  bool lofi_preview_via_flag_or_field_trial =
+      params::AreLoFiPreviewsEnabledViaFlags() ||
+      params::IsIncludedInLoFiPreviewFieldTrial();
+
   std::string header_value;
 
   // User is using Lo-Fi and not part of the "Control" group.
   if (request_info->IsUsingLoFi() && lofi_enabled_via_flag_or_field_trial) {
     if (headers->HasHeader(chrome_proxy_header())) {
       headers->GetHeader(chrome_proxy_header(), &header_value);
       headers->RemoveHeader(chrome_proxy_header());
       header_value += ", ";
     }
-    header_value += chrome_proxy_lo_fi_directive();
+
+    // Only add the "q=preview" directive on mainframe requests. Otherwise,
+    // add "q=low"
+    if (lofi_preview_via_flag_or_field_trial &&
+        (request.load_flags() & net::LOAD_MAIN_FRAME)) {
+      header_value += chrome_proxy_lo_fi_preview_directive();
+    } else {
+      header_value += chrome_proxy_lo_fi_directive();
+    }
+
     headers->SetHeader(chrome_proxy_header(), header_value);
     return true;
   }
 
   // User is part of Lo-Fi active control experiment.
   if (request_info->IsUsingLoFi() &&
       params::IsIncludedInLoFiControlFieldTrial()) {
     if (headers->HasHeader(chrome_proxy_header())) {
       headers->GetHeader(chrome_proxy_header(), &header_value);
       headers->RemoveHeader(chrome_proxy_header());
       header_value += ", ";
     }
     header_value += chrome_proxy_lo_fi_experiment_directive();
     headers->SetHeader(chrome_proxy_header(), header_value);
   }
 
   return false;
 }
 
 }  // namespace data_reduction_proxy