[Sync] Add favicon datatype proto support

sync/protocol/nigori_specifics.proto

 // Copyright (c) 2012 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.
 //
 // Sync protocol datatype extension for nigori keys.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 98 matching lines @@
   optional int64 keystore_migration_time = 32;
 
   // The time (in epoch milliseconds) at which a custom passphrase was set.
   // Note: this field may not be set if the custom passphrase was applied before
   // this field was introduced.
   optional int64 custom_passphrase_time = 33;
 
   // Boolean corresponding to whether custom spelling dictionary should be
   // encrypted.
   optional bool encrypt_dictionary = 34;
+
+  // Boolean corresponding to Whether to encrypt favicons data or not.
+  optional bool encrypt_favicons = 35;
 }