Add new permission string for extensions that override new tab pages.

chrome/common/extensions/permissions/chrome_permission_message_provider.cc

 // 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.
 
 #include "chrome/common/extensions/permissions/chrome_permission_message_provider.h"
 
 #include <vector>
 
 #include "base/metrics/field_trial.h"
 #include "base/stl_util.h"
@@ skipping 177 matching lines @@
   // TODO(treib,devlin): Remove this for M56, when hopefully all users will have
   // updated prefs.
   const APIPermission::ID kSettingsOverrideIDs[] = {
       APIPermission::kHomepage, APIPermission::kSearchProvider,
       APIPermission::kStartupPages};
   for (auto id : kSettingsOverrideIDs) {
     DropPermissionParameter(id, &old_ids);
     DropPermissionParameter(id, &new_ids);
   }
 
+  // For M62, we added a new permission ID for new tab page overrides. Consider
+  // the addition of this permission to not result in a privilege increase for
+  // the time being.
+  // TODO(robertshield): Remove this once most of the population is on M62+
+  new_ids.erase(APIPermission::kNewTabPageOverride);
+
   // If all the IDs were already there, it's not a privilege increase.
   if (old_ids.Includes(new_ids))
     return false;
 
   // Otherwise, check the actual messages - not all IDs result in a message,
   // and some messages can suppress others.
   PermissionMessages old_messages = GetPermissionMessages(old_ids);
   PermissionMessages new_messages = GetPermissionMessages(new_ids);
 
   ComparablePermissions old_strings(old_messages.begin(), old_messages.end());
@@ skipping 34 matching lines @@
   std::set<std::string> old_hosts_set(
       permission_message_util::GetDistinctHosts(old_list, false, false));
   std::set<std::string> new_hosts_only =
       base::STLSetDifference<std::set<std::string> >(new_hosts_set,
                                                      old_hosts_set);
 
   return !new_hosts_only.empty();
 }
 
 }  // namespace extensions