[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 bd3232a751830cc6cf921feb585e12afd66f40e5..2734ac1bc9865643cc809b6c6c6e5fc62033cb92 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
@@ -115,7 +115,7 @@ class TabNavigation {
 // SessionTab corresponds to a NavigationController.
 struct SessionTab {
   SessionTab();
-  ~SessionTab();
+  virtual ~SessionTab();
 
   // Unique id of the window.
   SessionID window_id;