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

sync/protocol/attachments.proto

-// Copyright 2014 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 for attachments.
-
-// Update proto_{value,enum}_conversions{.h,.cc,_unittest.cc} if you change any
-// fields in this file.
-
-syntax = "proto2";
-
-option optimize_for = LITE_RUNTIME;
-option retain_unknown_fields = true;
-
-package sync_pb;
-
-// Identifies an attachment.
-message AttachmentIdProto {
-  // Uniquely identifies the attachment. Two attachments with the same unique_id
-  // are considered equivalent.
-  optional string unique_id = 1;
-  // Size of the attachment data in bytes.
-  optional uint64 size_bytes = 2;
-  // Crc32c of the attachment data.
-  optional uint32 crc32c = 3;
-}
-
-// Metadata for a single attachment.
-message AttachmentMetadataRecord {
-  optional AttachmentIdProto id = 1;
-  // Indicates we know this attachment exists on the server.
-  optional bool is_on_server = 2;
-}
-
-// A collection of attachment metadata. This proto is part of EntryKernel's "on
-// disk" representation. Private to sync.
-message AttachmentMetadata {
-  // One record per attachment.
-  repeated AttachmentMetadataRecord record = 1;
-}