[NTP OptOut] Enable NTP article suggestions expanebale header by default

Bug: 850996
Change-Id: I20e1fa1e03c8c55d41f5a5a4e77f3c5059500b86
Reviewed-on: https://chromium-review.googlesource.com/1107306Reviewed-by: Filip Gorski <fgorski@chromium.org>
Commit-Queue: Becky Zhou <huayinz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568874}

components/ntp_snippets/features.cc

@@ -35,7 +35,7 @@ const base::Feature* const kAllFeatures[] = {
     &kRemoteSuggestionsBackendFeature};
 
 const base::Feature kArticleSuggestionsExpandableHeader{
-    "NTPArticleSuggestionsExpandableHeader", base::FEATURE_DISABLED_BY_DEFAULT};
+    "NTPArticleSuggestionsExpandableHeader", base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kArticleSuggestionsFeature{
     "NTPArticleSuggestions", base::FEATURE_ENABLED_BY_DEFAULT};