Warn users about potentially unwanted downloads.

chrome/common/extensions/api/downloads.idl

 // Copyright (c) 2012 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.
 
 // Use the <code>chrome.downloads</code> API to programmatically initiate,
 // monitor, manipulate, and search for downloads.
 [permissions=downloads]
 namespace downloads {
   [inline_doc] dictionary HeaderNameValuePair {
     // Name of the HTTP header.
@@ skipping 58 matching lines @@
   //     <dt>url</dt>
   //     <dd>The download's URL is known to be malicious.</dd>
   //     <dt>content</dt>
   //     <dd>The downloaded file is known to be malicious.</dd>
   //     <dt>uncommon</dt>
   //     <dd>The download's URL is not commonly downloaded and could be
   //     dangerous.</dd>
   //     <dt>host</dt>
   //     <dd>The download came from a host known to distribute malicious
   //     binaries and is likely dangerous.</dd>
+  //     <dt>unwanted</dt>
+  //     <dd>The download is potentially unwanted or unsafe. E.g. it could make
+  //     changes to browser or system settings.</dd>
   //     <dt>safe</dt>
   //     <dd>The download presents no known danger to the user's computer.</dd>
   //     <dt>accepted</dt>
   //     <dd>The user has accepted the dangerous download.</dd>
   // </dl>
-  enum DangerType {file, url, content, uncommon, host, safe, accepted};
+  enum DangerType {file, url, content, uncommon, host, unwanted, safe, accepted};
 
   // <dl><dt>in_progress</dt>
   //     <dd>The download is currently receiving data from the server.</dd>
   //     <dt>interrupted</dt>
   //     <dd>An error broke the connection with the file host.</dd>
   //     <dt>complete</dt>
   //     <dd>The download completed successfully.</dd>
   // </dl>
   enum State {in_progress, interrupted, complete};
 
@@ skipping 375 matching lines @@
     // <code>suggestion</code> object to <code>suggest</code> wins. In order to
     // avoid confusion regarding which extension will win, users should not
     // install extensions that may conflict. If the download is initiated by
     // $ref:download and the target filename is known before the MIME type and
     // tentative filename have been determined, pass <code>filename</code> to
     // $ref:download instead.
     [maxListeners=1] static void onDeterminingFilename(
         DownloadItem downloadItem, SuggestFilenameCallback suggest);
   };
 };