[Sync] Add per-navigation timestamps/unique ids to tab sync.

chrome/browser/sessions/session_types.h

Index: chrome/browser/sessions/session_types.h
diff --git a/chrome/browser/sessions/session_types.h b/chrome/browser/sessions/session_types.h
index e56ff3c73d2ca01a72c3ee5d5b014f876a60540d..11b4abb2307c03d747d20df3a499e860e02cddf6 100644
--- a/chrome/browser/sessions/session_types.h
+++ b/chrome/browser/sessions/session_types.h
@@ -45,7 +45,7 @@ class TabNavigation {
                 const std::string& state,
                 content::PageTransition transition);
   TabNavigation(const TabNavigation& tab);
-  ~TabNavigation();
+  virtual ~TabNavigation();
   TabNavigation& operator=(const TabNavigation& tab);
 
   // Converts this TabNavigation into a NavigationEntry with a page id of
@@ -122,7 +122,7 @@ class TabNavigation {
 // SessionTab corresponds to a NavigationController.
 struct SessionTab {
   SessionTab();
-  ~SessionTab();
+  virtual ~SessionTab();
 
   // Unique id of the window.
   SessionID window_id;