MD History: promote menu button to show clear browsing data in narrow mode

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index b684057cab3282afbf2918f13dc25c02b36c48e9..377594723bab4b02e9e0ee9a2525f8d871ea71e6 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -930,6 +930,12 @@ const char kSavingBrowserHistoryDisabled[] = "history.saving_disabled";
 // permitted.
 const char kAllowDeletingBrowserHistory[] = "history.deleting_enabled";
 
+#if !defined(OS_ANDROID) && !defined(OS_IOS)
+// Whether the "Click here to clear your browsing data" tooltip promo has been
+// shown on the Material Design History page.
+const char kMdHistoryMenuPromoShown[] = "history.menu_promo_shown";
+#endif
+
 // Boolean controlling whether SafeSearch is mandatory for Google Web Searches.
 const char kForceGoogleSafeSearch[] = "settings.force_google_safesearch";