Add a new SBThreatType for the harmful download interstitial

BUG=397754
R=mattm@chromium.org

Review URL: https://codereview.chromium.org/578103002

Cr-Commit-Position: refs/heads/master@{#295852}

chrome/browser/safe_browsing/safe_browsing_util.h

@@ -132,6 +132,9 @@ enum SBThreatType {
   // The URL hosts malware.
   SB_THREAT_TYPE_URL_MALWARE,
 
+  // The URL hosts harmful programs.
+  SB_THREAT_TYPE_URL_HARMFUL,
+
   // The download URL is malware.
   SB_THREAT_TYPE_BINARY_MALWARE_URL,