[Payments] Put Web Payments feature on desktop behind flag

content/public/common/content_features.cc

Index: content/public/common/content_features.cc
diff --git a/content/public/common/content_features.cc b/content/public/common/content_features.cc
index 94b685d185a2b36400d5cdc6be9021103263195e..8f7cb7b005a15de94cef818afb4c4359aa504113 100644
--- a/content/public/common/content_features.cc
+++ b/content/public/common/content_features.cc
@@ -286,7 +286,10 @@ const base::Feature kServiceWorkerPaymentApps{
 // The JavaScript API for payments on the web.
 const base::Feature kWebPayments{"WebPayments",
                                  base::FEATURE_ENABLED_BY_DEFAULT};
-
+#else
+// The JavaScript API for payments on the web.
+const base::Feature kWebPayments{"WebPayments",
+                                 base::FEATURE_DISABLED_BY_DEFAULT};
 #endif
 
 #if !defined(OS_ANDROID)