Add taskid for navigation, created in session sync

components/sync/protocol/session_specifics.proto

Index: components/sync/protocol/session_specifics.proto
diff --git a/components/sync/protocol/session_specifics.proto b/components/sync/protocol/session_specifics.proto
index 0c8095d2233ef791c9627d4a028e3d5c3e8a4b8a..4039bbd453ee88a54230e8b75955073333849922 100644
--- a/components/sync/protocol/session_specifics.proto
+++ b/components/sync/protocol/session_specifics.proto
@@ -156,6 +156,18 @@ message TabNavigation {
   }
   // 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.