Add feature to control showing suggestion summaries.

BUG=720288

Review-Url: https://codereview.chromium.org/2874773002
Cr-Commit-Position: refs/heads/master@{#470569}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 09ce9a435..c5ebda3d 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2267,6 +2267,11 @@
      flag_descriptions::kEnableContentSuggestionsSettingsDescription,
      kOsAndroid,
      FEATURE_VALUE_TYPE(chrome::android::kContentSuggestionsSettings)},
+    {"enable-content-suggestions-show-summary",
+     flag_descriptions::kEnableContentSuggestionsShowSummaryName,
+     flag_descriptions::kEnableContentSuggestionsShowSummaryDescription,
+     kOsAndroid,
+     FEATURE_VALUE_TYPE(chrome::android::kContentSuggestionsShowSummary)},
     {"enable-ntp-remote-suggestions",
      flag_descriptions::kEnableNtpRemoteSuggestionsName,
      flag_descriptions::kEnableNtpRemoteSuggestionsDescription, kOsAndroid,