Adds SB V4 response handler to Protocol Manager.

components/safe_browsing_db/util.h

Index: components/safe_browsing_db/util.h
diff --git a/components/safe_browsing_db/util.h b/components/safe_browsing_db/util.h
index daa202ef8c9a072cdab5bf19eb6fe1e113afc95a..d2e46ee68fd14ada187b6db82257b3ea61fa8944 100644
--- a/components/safe_browsing_db/util.h
+++ b/components/safe_browsing_db/util.h
@@ -65,6 +65,9 @@ struct SBFullHashResult {
   // TODO(shess): Refactor to allow ListType here.
   int list_id;
   std::string metadata;
+  // Used only for V4 results. The cache lifetime for this result. The response
+  // must not be cached for more than this duration to avoid false positives.
+  base::TimeDelta cache_duration;
 };
 
 // Caches individual response from GETHASH request.