[Offline Pages] Enable CT features by default.

This is more of a kill switch than a feature flag, so it deserves to be
enabled until deemed harmful.

BUG=

Review-Url: https://codereview.chromium.org/2273873002
Cr-Commit-Position: refs/heads/master@{#414225}

components/offline_pages/offline_page_feature.cc

@@ -23,7 +23,7 @@ const base::Feature kOfflinePagesBackgroundLoadingFeature {
 };
 
 const base::Feature kOfflinePagesCTFeature {
-   "OfflinePagesCT", base::FEATURE_DISABLED_BY_DEFAULT
+   "OfflinePagesCT", base::FEATURE_ENABLED_BY_DEFAULT
 };
 
 const base::Feature kOfflinePagesSharingFeature{