Allow SessionService to be disabled.

chrome/browser/sessions/tab_restore_service.cc

Index: chrome/browser/sessions/tab_restore_service.cc
diff --git a/chrome/browser/sessions/tab_restore_service.cc b/chrome/browser/sessions/tab_restore_service.cc
index 2fee862545e98a6200a60a252d13ca25373a034d..701b0a30db928c720aa4b1c22b32121937709d97 100644
--- a/chrome/browser/sessions/tab_restore_service.cc
+++ b/chrome/browser/sessions/tab_restore_service.cc
@@ -439,6 +439,11 @@ void TabRestoreService::LoadTabsFromLastSession() {
   if (load_state_ != NOT_LOADED || entries_.size() == kMaxEntries)
     return;
 
+#if !defined(ENABLE_SESSION_SERVICE)
+  // If sessions are not stored in the SessionService, default to
+  // |LOADED_LAST_SESSION| state.
+  load_state_ = LOADING | LOADED_LAST_SESSION;
+#else
   load_state_ = LOADING;
 
   SessionService* session_service =
@@ -455,6 +460,7 @@ void TabRestoreService::LoadTabsFromLastSession() {
   } else {
     load_state_ |= LOADED_LAST_SESSION;
   }
+#endif
 
   // Request the tabs closed in the last session. If the last session crashed,
   // this won't contain the tabs/window that were open at the point of the