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;
+
+  // Id of the task associated with this navigation.
+  optional TaskId task_id = 27;
+}
+
+// Task id which recursively encodes id of its parent task. From one task id,
+// we can get ids of its all ancester tasks.

[Nicolas Zea, 2017/03/27 20:43:52]

Explain what a task node id is (namely a GUID that defines a specific navigation
that matches global_id above)

[shenchao, 2017/04/06 00:54:55]

Done.

+// E.g. if current task id is
+// {
+//   task_node_id:1
+//   task_node_id:2
+//   task_node_id:3
+// }, then id of its parent task is
+// {
+//   task_node_id:1
+//   task_node_id:2
+// }, and id of its grandparent task, which is a root task is
+// {
+//   task_node_id:1
+// }
+message TaskId {
+  // A list of node ids, not encoding parent node, for task path of (root,
+  // ..., parent, current task).
+  repeated int64 task_node_id = 1;

[Nicolas Zea, 2017/03/27 20:43:52]

Should we bother encoding the current task id/ It's basically going to be the
same as the global id above right?

[shenchao, 2017/04/04 18:37:50]

Just found we can't use global_id, which changes when the page is visited via
forward_back. But we want to keep task_node_id same for different visits over
time, right?

 }
 
 // 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;
 }