Bug 1567273 - Pref to enable lang config for Discovery Stream layouts r=gvn

Differential Revision: https://phabricator.services.mozilla.com/D53236

--HG--
extra : moz-landing-system : lando

browser/app/profile/firefox.js

@@ -1307,6 +1307,8 @@ pref("browser.newtabpage.activity-stream.asrouter.useRemoteL10n", true);
 pref("browser.newtabpage.activity-stream.discoverystream.enabled", true);
 pref("browser.newtabpage.activity-stream.discoverystream.hardcoded-basic-layout", false);
 pref("browser.newtabpage.activity-stream.discoverystream.spocs-endpoint", "");
+// List of langs that get the 7 row layout.
+pref("browser.newtabpage.activity-stream.discoverystream.lang-layout-config", "en");
 
 // The pref controls if search hand-off is enabled for Activity Stream.
 #ifdef NIGHTLY_BUILD