Add feature to control showing suggestion summaries.

chrome/browser/flag_descriptions.cc

Index: chrome/browser/flag_descriptions.cc
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 2d865dfe2d36505e861f9f6f2c56ff312d8eaf44..98b256abc29a5bd765eab35827ec54e9e89a1005 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -2383,6 +2383,12 @@ const char kEnableContentSuggestionsSettingsDescription[] =
     "If enabled, the content suggestions settings will be available from the "
     "main settings menu.";
 
+const char kEnableContentSuggestionsShowSummaryName[] =
+    "Show content suggestions summaries.";
+
+const char kEnableContentSuggestionsShowSummaryDescription[] =
+    "If enabled, the content suggestions summaries will be shown.";
+
 const char kEnableNtpRemoteSuggestionsName[] =
     "Show server-side suggestions on the New Tab page";