[Sync] Maintain a global_id mapping to update UserEvents that references navigations

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 86 matching lines @@
   // state of the page. This includes form entries and scroll position for each
   // frame.
   // optional string state = 5;  // obsolete.
   // The core transition type.
   optional SyncEnums.PageTransition page_transition = 6 [default = TYPED];
   // If this transition was triggered by a redirect, the redirect type.
   optional SyncEnums.PageTransitionRedirectType redirect_type = 7;
   // The unique navigation id (within this client).
   optional int32 unique_id = 8;
   // Timestamp for when this navigation last occurred (in client time).
-  // If the user goes back/foward in history the timestamp may refresh.
+  // If the user goes back/forward in history the timestamp may refresh.
   optional int64 timestamp_msec = 9;
   // User used the Forward or Back button to navigate among browsing history.
   optional bool navigation_forward_back = 10;
   // User used the address bar to trigger this navigation.
   optional bool navigation_from_address_bar = 11;
   // User is navigating to the home page.
   optional bool navigation_home_page = 12;
   // The beginning of a navigation chain.
   optional bool navigation_chain_start = 13;
   // The last transition in a redirect chain.
@@ skipping 49 matching lines @@
   // 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;
 }