[Sync] Add a new global_id field to sync_pb::TabNavigation

chrome/browser/sessions/session_types.cc

Index: chrome/browser/sessions/session_types.cc
diff --git a/chrome/browser/sessions/session_types.cc b/chrome/browser/sessions/session_types.cc
index 183b3a90d54ad386be8772babc83af166e5080c3..f89af4f1f418afef2ff1defde6ee0d83697d948f 100644
--- a/chrome/browser/sessions/session_types.cc
+++ b/chrome/browser/sessions/session_types.cc
@@ -414,9 +414,9 @@ sync_pb::TabNavigation TabNavigation::ToSyncData() const {
       (transition_type_ & content::PAGE_TRANSITION_CHAIN_END) != 0);
 
   sync_data.set_unique_id(unique_id_);
-  // TODO(akalin): Don't lose resolution, i.e. define a new timestamp
-  // field with microsecond resolution and use that.
   sync_data.set_timestamp(syncer::TimeToProtoTime(timestamp_));
+  // The full-resolution timestamp works as a global ID.
+  sync_data.set_global_id(timestamp_.ToInternalValue());
 
   return sync_data;
 }