[SyncFS] Add FileMetadata and FileTracker message

chrome/browser/sync_file_system/drive_backend/metadata_database.proto

 // 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.
 //
 // Protocol buffer definitions for Drive backend of Syncable FileSystem.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package sync_file_system.drive_backend;
 
 enum FileKind {
   KIND_UNSUPPORTED = 0;
   KIND_FILE = 1;
   KIND_FOLDER = 2;
 }
 
 message ServiceMetadata {
   optional int64 largest_change_id = 1;
-  optional string sync_root_folder_id = 2;
+  optional int64 sync_root_tracker_id = 2;
+
+  // The sequence number of FileTrackers. Must be positive.
+  optional int64 next_tracker_id = 3;
 }
+
+// Holds details of file/folder metadata.
+message FileDetails {
+  repeated string parent_folder_ids = 1;
+
+  optional string title = 2;
+  optional FileKind kind = 3;
+  optional string md5 = 4;
+  optional string etag = 5;
+
+  // Creation time and modification time of the resource.
+  // Serialized by Time::ToInternalValue.
+  optional int64 creation_time = 6;
+  optional int64 modification_time = 7;
+
+  optional bool deleted = 8;
+  optional int64 change_id = 9;
+}
+
+// Represents a server-side file.
+message FileMetadata {
+  // File ID of the remote file/folder which the FileMetadata represents.
+  required string file_id = 1;
+
+  optional FileDetails details = 2;
+}
+
+// Represents synced local file.
+message FileTracker {
+  // A unique sequence number to identify the tracker. Must be positive.
+  required int64 tracker_id = 1;
+
+  // Points the parent tracker in the tracker tree.  0 if there's no parent.
+  required int64 parent_tracker_id = 2;
+
+  required string file_id = 3;
+
+  optional string app_id = 4;
+  optional bool is_app_root = 5;
+
+  optional FileDetails synced_details = 6;
+
+  // True if the file is changed since the last update for this file.
+  optional bool dirty = 7;
+
+  // True if the FileTracker is active.
+  // Remote file modification should only be applied to active trackers.
+  // Active FileTracker must have a unique title under its parent.
+  optional bool active = 8;
+
+  // Valid only for folders.
+  // True if the folder contents have not yet been fetched.
+  optional bool needs_folder_listing = 9;
+}