[Session restore] Add MRU logic to loading of background pages.

chrome/browser/sessions/tab_restore_service.h

Index: chrome/browser/sessions/tab_restore_service.h
diff --git a/chrome/browser/sessions/tab_restore_service.h b/chrome/browser/sessions/tab_restore_service.h
index ccf2d2ab73c452b11edd6e18d7841d9fc3750a19..8624f1948530e05099b2e2324e2210529f871f56 100644
--- a/chrome/browser/sessions/tab_restore_service.h
+++ b/chrome/browser/sessions/tab_restore_service.h
@@ -105,6 +105,9 @@ class TabRestoreService : public KeyedService {
 
     // The user agent override used for the tab's navigations (if applicable).
     std::string user_agent_override;
+
+    // Timestamp of the last time the tab was active.
+    base::TimeTicks last_active_time;
   };
 
   // Represents a previously open window.