Add taskid for navigation, created in session sync

components/sync/protocol/session_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 sessions.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 138 matching lines @@
   // third_party/WebKit/public/platform/WebReferrerPolicy.h.
   optional int32 correct_referrer_policy = 25 [default = 1];
 
   enum PasswordState {
     PASSWORD_STATE_UNKNOWN = 0;
     NO_PASSWORD_FIELD = 1;
     HAS_PASSWORD_FIELD = 2;
   }
   // Whether the Password Manager saw a password field on the page.
   optional PasswordState password_state = 26;
+
+  // The id for the task associated with this navigation, which is globally
+  // unique with high probability.
+  // Similar with global_id, but used to identify a navigation in Chrome Tasks,
+  // so navigations of a page have the same task_id if one is the first visit of
+  // the page, and others are its back/forward visits.
+  optional int64 task_id = 27;
+  // Task ids of all ancestor navigations, which can be from other tabs, from
+  // root to parent. We define navigation A is parent of navigation B if page of
+  // B is got by clicking a link on page of A. This relationship is used to
+  // define a Chrome Task as a tree rooted by a navigation.
+  repeated int64 ancestor_task_id = 28;
 }
 
 // Navigation information for a single redirection within a single navigation.
 message NavigationRedirect {
   // A URL that redirected while navigating to the virtual_url.
   optional string url = 1;
 }