Warn users about potentially unwanted downloads.

tools/metrics/histograms/histograms.xml

 <!--
 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.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 15434 matching lines @@
 
 <enum name="DownloadItem.DangerType" type="int">
   <int value="0" label="NOT_DANGEROUS"/>
   <int value="1" label="DANGEROUS_FILE"/>
   <int value="2" label="DANGEROUS_URL"/>
   <int value="3" label="DANGEROUS_CONTENT"/>
   <int value="4" label="MAYBE_DANGEROUS_CONTENT"/>
   <int value="5" label="UNCOMMON_CONTENT"/>
   <int value="6" label="USER_VALIDATED"/>
   <int value="7" label="DANGEROUS_HOST"/>
+  <int value="8" label="POTENTIALLY_UNWANTED"/>
 </enum>
 
 <enum name="DownloadSavePackageEvent" type="int">
   <int value="0" label="Started"/>
   <int value="1" label="Cancelled"/>
   <int value="2" label="Finished"/>
   <int value="3" label="Write to already completed file"/>
   <int value="4" label="Write to already failed file"/>
 </enum>
 
@@ skipping 7951 matching lines @@
   <group name="Disabled" label="Neither extra webstore link is visible"/>
   <group name="FooterLink" label="Link in bottom right of footer"/>
   <group name="PlusIcon" label="Plus icon in apps page"/>
   <affected-histogram name="Extensions.AppLaunch"/>
   <affected-histogram name="NewTabPage.DefaultPageType"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>