Measure usage metrics to prepare for adaptive fetching rates in M55

components/ntp_snippets/pref_names.h

Index: components/ntp_snippets/pref_names.h
diff --git a/components/ntp_snippets/pref_names.h b/components/ntp_snippets/pref_names.h
index 8153cac627e42ebeb1f7345a7f00e3a2f33b5823..572530229727627755c2ca88e908754fee17a791 100644
--- a/components/ntp_snippets/pref_names.h
+++ b/components/ntp_snippets/pref_names.h
@@ -35,6 +35,23 @@ extern const char kDismissedDownloadSuggestions[];
 // The pref name for the time when M54 was first started on the device.
 extern const char kBookmarksFirstM54Start[];
 
+// The pref name for the discounted average number of hours between opening a
+// new NTP.
+extern const char kUserClassifierAverageHoursToOpenNTP[];
+// The pref name for the discounted average number of hours between showing
+// content suggestions.
+extern const char kUserClassifierAverageHoursToShowSuggestions[];
+// The pref name for the discounted average number of hours between using
+// content suggestions (i.e. opening one or clicking on the "More" button).
+extern const char kUserClassifierAverageHoursToUseSuggestions[];
+
+// The pref name for the last time a new NTP was opened.
+extern const char kUserClassifierLastTimeToOpenNTP[];
+// The pref name for the last time content suggestions were shown to the user.
+extern const char kUserClassifierLastTimeToShowSuggestions[];
+// The pref name for the last time content suggestions were used by the user.
+extern const char kUserClassifierLastTimeToUseSuggestions[];
+
 }  // namespace prefs
 }  // namespace ntp_snippets