Add feature to control showing suggestion summaries.

chrome/browser/flag_descriptions.h

Index: chrome/browser/flag_descriptions.h
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 0e28065dd02dc01e4841ff413ba09e5918581596..76d93a554be15f0fa35847d2562663c5607678f9 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -2606,6 +2606,13 @@ extern const char kEnableContentSuggestionsSettingsName[];
 // suggestions.
 extern const char kEnableContentSuggestionsSettingsDescription[];
 
+// Name for the flag to enable showing the summary for content suggestions.
+extern const char kEnableContentSuggestionsShowSummaryName[];
+
+// Description for the flag to enable showing the summary for content
+// suggestions.
+extern const char kEnableContentSuggestionsShowSummaryDescription[];
+
 // Name for the flag to enable server-side suggestions on the New Tab Page.
 extern const char kEnableNtpRemoteSuggestionsName[];