[Downloads] Gracefully handle SafeBrowsing check failures.

chrome/browser/download/download_target_info.h

 // Copyright 2013 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_TARGET_INFO_H_
 #define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_TARGET_INFO_H_
 
 #include "base/files/file_path.h"
 #include "content/public/browser/download_danger_type.h"
 #include "content/public/browser/download_item.h"
 
 struct DownloadTargetInfo {
   DownloadTargetInfo();
   ~DownloadTargetInfo();
 
   // Final full target path of the download. Must be non-empty for the remaining
   // fields to be considered valid. The path is a local file system path. Any
   // existing file at this path should be overwritten.
   base::FilePath target_path;
 
   // Disposition. This will be TARGET_DISPOSITION_PROMPT if the user was
   // prompted during the process of determining the download target. Otherwise
   // it will be TARGET_DISPOSITION_OVERWRITE.
   content::DownloadItem::TargetDisposition target_disposition;
 
   // Danger type of the download.
   content::DownloadDangerType danger_type;
 
+  // The danger type of the download could be set to MAYBE_DANGEROUS_CONTENT if
+  // the file type is handled by SafeBrowsing. However, if the SafeBrowsing
+  // service is unable to verify whether the file is safe or not, we are on our
+  // own. This flag indicates whether the download should be considered
+  // dangerous if SafeBrowsing returns an unknown verdict.
+  //
+  // Note that some downloads (e.g. "Save link as" on a link to a binary) would
+  // not be considered 'Dangerous' even if SafeBrowsing came back with an
+  // unknown verdict. So we can't always show a warning when SB fails.
+  bool is_dangerous_file;
+
   // Suggested intermediate path. The downloaded bytes should be written to this
   // path until all the bytes are available and the user has accepted a
   // dangerous download. At that point, the download can be renamed to
   // |target_path|.
   base::FilePath intermediate_path;
 
   // MIME type based on the file type of the download. This may be different
   // from DownloadItem::GetMimeType() since the latter is based on the server
   // response, and this one is based on the filename.
   std::string mime_type;
 
   // Whether the |target_path| would be handled safely by the browser if it were
   // to be opened with a file:// URL. This can be used later to decide how file
   // opens should be handled. The file is considered to be handled safely if the
   // filetype is supported by the renderer or a sandboxed plug-in.
   bool is_filetype_handled_safely;
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_TARGET_INFO_H_