[Sync] USS: Ignore encryption changes during conflict resolution 1/2

sync/protocol/entity_metadata.proto

 // Copyright 2015 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 option retain_unknown_fields = true;
 
 package sync_pb;
@@ skipping 34 matching lines @@
   // Entity creation and modification timestamps.
   // Assigned by the client and synced by the server, though the server usually
   // doesn't bother to inspect their values.
   optional int64 creation_time = 7;
   optional int64 modification_time = 8;
 
   // A hash of the current entity specifics value. Used to detect whether
   // entity's specifics value has changed without having to keep specifics in
   // memory.
   optional string specifics_hash = 9;
+
+  // A hash of the last specifics known by both the client and server. Used to
+  // detect when local commits and remote updates are just for encryption. This
+  // value will be the empty string only in the following cases: the entity is
+  // in sync with the server, has never been synced, or is deleted.
+  optional string base_specifics_hash = 10;
 }