Do not trigger Lo-Fi on main frame requests

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"
@@ skipping 49 matching lines @@
   std::string header_value;
 
   if (headers->HasHeader(chrome_proxy_header())) {
     headers->GetHeader(chrome_proxy_header(), &header_value);
     headers->RemoveHeader(chrome_proxy_header());
     header_value += ", ";
   }
 
   // If in the preview field trial or the preview flag is enabled, only add the
   // "q=preview" directive on main frame requests. Do not add Lo-Fi directives
-  // to other requests when previews are enabled. If previews are not enabled,
-  // add "q=low".
+  // to other requests when previews are enabled.
   if (lofi_preview_via_flag_or_field_trial) {
     if (request.load_flags() & net::LOAD_MAIN_FRAME) {
       if (params::AreLoFiPreviewsEnabledViaFlags()) {
         header_value += chrome_proxy_lo_fi_ignore_preview_blacklist_directive();
         header_value += ", ";
       }
       header_value += chrome_proxy_lo_fi_preview_directive();
     }
-  } else {
+  } else if (!(request.load_flags() & net::LOAD_MAIN_FRAME)) {
+    // If previews are not enabled, add "q=low" for requests that are not main
+    // frame.
     header_value += chrome_proxy_lo_fi_directive();
   }
 
-  // |header_value| may be empty because the Lo-Fi directive is not added
-  // to subrequests when preview mode is enabled.
   if (!header_value.empty())
     headers->SetHeader(chrome_proxy_header(), header_value);
 
   return true;
 }
 
 }  // namespace data_reduction_proxy