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..14f0d9311f7ff5603148874868e5a039ab4eb8b1 100644
--- a/components/ntp_snippets/pref_names.h
+++ b/components/ntp_snippets/pref_names.h
@@ -35,6 +35,24 @@ 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 browsing sessions per hour
+// that involve opening a new NTP.
+extern const char kUserClassifierAverageNTPOpenedPerHour[];
+// The pref name for the discounted average number of browsing sessions per hour
+// that involve opening showing the content suggestions.
+extern const char kUserClassifierAverageSuggestionsShownPerHour[];
+// The pref name for the discounted average number of browsing sessions per hour
+// that involve using content suggestions (i.e. opening one or clicking on the
+// "More" button).
+extern const char kUserClassifierAverageSuggestionsUsedPerHour[];
+
+// 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