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

components/data_reduction_proxy/core/common/lofi_decider.h

 // 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.
 
 #ifndef COMPONENTS_DATA_REDUCTION_PROXY_CORE_BROWSER_LOFI_DECIDER_H_
 #define COMPONENTS_DATA_REDUCTION_PROXY_CORE_BROWSER_LOFI_DECIDER_H_
 
 #include "base/macros.h"
 #include "net/url_request/url_request.h"
 
 namespace net {
 class HttpRequestHeaders;
 }
 
 namespace data_reduction_proxy {
 
 // Interface to determine if a request should be made for a low fidelity version
 // of the resource.
 class LoFiDecider {
  public:
   virtual ~LoFiDecider() {}
 
   // Returns true when Lo-Fi mode is on for the given |request|. This means the
   // Lo-Fi header should be added to the given request.
   virtual bool IsUsingLoFiMode(const net::URLRequest& request) const = 0;
 
   // Returns true when Lo-Fi mode is on for the given |request|. If the
   // |request| is using Lo-Fi mode, adds the "q=low" directive to the |headers|.
-  // If the user is in the experiment control group and Lo-Fi is on, adds the
-  // experiment directive "exp=lofi_active_control".
+  // If the |request| is using Lo-Fi preview mode, and it is a main frame
+  // request adds the "q=preview" and it is a main frame request directive to
+  // the |headers|. If the user is in the experiment control group and Lo-Fi is
+  // on, adds the experiment directive "exp=lofi_active_control".
   virtual bool MaybeAddLoFiDirectiveToHeaders(
       const net::URLRequest& request,
       net::HttpRequestHeaders* headers) const = 0;
 };
 
 }  // namespace data_reduction_proxy
 
 #endif  // COMPONENTS_DATA_REDUCTION_PROXY_CORE_BROWSER_LOFI_DECIDER_H_