Adding a parameter for previews NQE triggering threshold

components/previews/core/previews_experiments.h

Index: components/previews/core/previews_experiments.h
diff --git a/components/previews/core/previews_experiments.h b/components/previews/core/previews_experiments.h
index 021db0a8de82139b99aa0c1b4b0c9159d582dde5..ad0bded4a856ee7de386c5c329e28415dd0504a2 100644
--- a/components/previews/core/previews_experiments.h
+++ b/components/previews/core/previews_experiments.h
@@ -6,6 +6,7 @@
 #define COMPONENTS_PREVIEWS_CORE_PREVIEWS_EXPERIMENTS_H_
 
 #include "base/time/time.h"
+#include "net/nqe/effective_connection_type.h"
 
 namespace previews {
 
@@ -43,6 +44,10 @@ base::TimeDelta SingleOptOutDuration();
 // shown as a preview.
 base::TimeDelta OfflinePreviewFreshnessDuration();
 
+// The threshold of EffectiveConnectionType above which previews should not be
+// served.
+net::EffectiveConnectionType EffectiveConnectionTypeThreshold();
+
 }  // namespace params
 
 enum class PreviewsType {