[Session restore] Rename group name Enabled to Restore.

TBR=sky@chromium.org
BUG=465815

Review URL: https://codereview.chromium.org/1062293004

Cr-Commit-Position: refs/heads/master@{#324154}

chrome/browser/sessions/session_restore_delegate.cc

@@ -17,7 +17,7 @@ void SessionRestoreDelegate::RestoreTabs(
   base::FieldTrial* trial =
       base::FieldTrialList::Find("SessionRestoreBackgroundLoading");
   bool active_only = true;
-  if (!trial || trial->group_name() == "Enabled") {
+  if (!trial || trial->group_name() == "Restore") {
     TabLoader::RestoreTabs(tabs, restore_started);
     active_only = false;
   }