Add chrome://flags entry to enable the standalone content suggestions UI.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 64d3ff7ac0f52319d920dd75785d623211564063..65a5b4f1172a803accd8390d8f6e1e441ea7e214 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -15169,6 +15169,12 @@ Please check your email at <ph name="ACCOUNT_EMAIL">$2<ex>jane.doe@gmail.com</ex
       <message name="IDS_FLAGS_ENABLE_NTP_FOREIGN_SESSIONS_SUGGESTIONS_DESCRIPTION" desc="Description for the flag to enable foreign sessions suggestions on the New Tab page." translateable="false">
         If enabled, the list of content suggestions on the New Tab page (see #enable-ntp-snippets) will contain recent foreign tabs.
       </message>
+      <message name="IDS_FLAGS_ENABLE_NTP_STANDALONE_SUGGESTIONS_UI_NAME" desc="Name for the flag to enable a standalone content suggestions UI." translateable="false">
+        Standalone content suggestions UI
+      </message>
+      <message name="IDS_FLAGS_ENABLE_NTP_STANDALONE_SUGGESTIONS_UI_DESCRIPTION" desc="Description for the flag to enable a standalone content suggestions UI." translateable="false">
+        Show a menu item to open a standalone content suggestions UI for testing.
+      </message>
     </if>
 
     <if expr="is_android">