V4Only: In V4Only mode use PVer4 for all SafeBrowsing operations

components/safe_browsing_db/v4_feature_list.h

 // Copyright 2016 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 COMPONENTS_SAFE_BROWSING_DB_V4_FEATURE_LIST_H_
 #define COMPONENTS_SAFE_BROWSING_DB_V4_FEATURE_LIST_H_
 
 namespace safe_browsing {
 
 // Exposes methods to check whether a particular feature has been enabled
 // through Finch.
 namespace V4FeatureList {
 
-// Is the PVer4 database manager enabled?
+// Is the PVer4 database manager enabled? Should be true if either of those
+// below are true.
 bool IsLocalDatabaseManagerEnabled();
 
 // Is the PVer4 database being checked for resource reputation? If this returns
 // true, use PVer4 database for CheckBrowseUrl, otherwise use PVer3.
 bool IsV4HybridEnabled();
 
+// Is only the PVer4 database being checked for resource reputation? If this
+// returns true, use PVer4 database for all SafeBrowsing operations, and don't
+// update the PVer3 database at all.  This is the launch configuration.
+bool IsV4OnlyEnabled();
+
 }  // namespace V4FeatureList
 
 }  // namespace safe_browsing
 
 #endif  // COMPONENTS_SAFE_BROWSING_DB_V4_FEATURE_LIST_H_