[Sync] Move //sync to //components/sync.

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;
-
-// Sync proto to store entity metadata in model type storage.
-message EntityMetadata {
-  // A hash based on the client tag and model type.
-  // Used for various map lookups. Should always be available.
-  // Sent to the server as SyncEntity::client_defined_unique_tag.
-  optional string client_tag_hash = 1;
-
-  // The entity's server-assigned ID.
-  //
-  // Prior to the item's first commit, we leave this value as an empty string.
-  // The initial ID for a newly created item has to meet certain uniqueness
-  // requirements, and we handle those on the sync thread.
-  optional string server_id = 2;
-
-  // Whether or not the entity is deleted.
-  optional bool is_deleted = 3;
-
-  // A version number used to track in-progress commits. Each local change
-  // increments this number.
-  optional int64 sequence_number = 4;
-
-  // The sequence number of the last item known to be successfully committed.
-  optional int64 acked_sequence_number = 5;
-
-  // The server version on which this item is based.
-  //
-  // If there are no local changes, this is the version of the entity as we see
-  // it here.
-  //
-  // If there are local changes, this is the version of the entity on which
-  // those changes are based.
-  optional int64 server_version = 6 [default = -1];
-
-  // 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;
-}