Change logic to enable for group Enabled (for A/B testing).

This allows to have multiple Disabled group, e.g. Disabled/Disabled_control, and thus eases experimentation.

TBR=sky@chromium.org
BUG=465815

Review URL: https://codereview.chromium.org/1062243002

Cr-Commit-Position: refs/heads/master@{#324099}

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() != "Disabled") {
+  if (!trial || trial->group_name() == "Enabled") {
     TabLoader::RestoreTabs(tabs, restore_started);
     active_only = false;
   }