For downloads requiring a user gesture, also require...

chrome/browser/download/download_state_info.h

 // Copyright (c) 2011 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 CHROME_BROWSER_DOWNLOAD_DOWNLOAD_STATE_INFO_H_
 #define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_STATE_INFO_H_
 #pragma once
 
 #include "base/file_path.h"
 
 // Contains information relating to the process of determining what to do with
 // the download.
 struct DownloadStateInfo {
+  enum Tristate { NO = 0, YES, UNKNOWN, };
   DownloadStateInfo();
   DownloadStateInfo(bool has_user_gesture,
                     bool prompt_user_for_save_location);
   DownloadStateInfo(const FilePath& target,
                     const FilePath& forced_name,
                     bool has_user_gesture,
                     bool prompt_user_for_save_location,
                     int uniquifier,
                     bool dangerous_file,
-                    bool dangerous_url,
+                    Tristate dangerous_url,
+                    Tristate visited_referrer_before,
                     bool extension_install);
 
   // Indicates if the download is dangerous.
   bool IsDangerous() const;
 
   // The original name for a dangerous download, specified by the request.
   FilePath target_name;
 
   // The path where we save the download.  Typically generated.
   FilePath suggested_path;
 
   // A number that should be added to the suggested path to make it unique.
   // 0 means no number should be appended.  It is eventually incorporated
   // into the final file name.
   int path_uniquifier;
 
   // True if the download is the result of user action.
   bool has_user_gesture;
 
   // True if we should display the 'save as...' UI and prompt the user
   // for the download location.
   // False if the UI should be suppressed and the download performed to the
   // default location.
   bool prompt_user_for_save_location;
 
   // True if this download file is potentially dangerous (ex: exe, dll, ...).
   bool is_dangerous_file;
 
   // If safebrowsing believes this URL leads to malware.
-  bool is_dangerous_url;
+  Tristate is_dangerous_url;
+
+  // If the user has visited the page hosting the download before today.
+  Tristate visited_referrer_before;
 
   // True if this download is for extension install.
   bool is_extension_install;
 
   // True if this download's file name was specified initially.
   FilePath force_file_name;
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_STATE_INFO_H_