Remove last usage functions from HostContentSettingsMap and clean up prefs

components/content_settings/core/browser/content_settings_pref.h

Index: components/content_settings/core/browser/content_settings_pref.h
diff --git a/components/content_settings/core/browser/content_settings_pref.h b/components/content_settings/core/browser/content_settings_pref.h
index d06fe01e28b5b7ee1c0da6e302c6451b260b0e2d..77c6d031fb1c6256122669d3547924a5959a654a 100644
--- a/components/content_settings/core/browser/content_settings_pref.h
+++ b/components/content_settings/core/browser/content_settings_pref.h
@@ -23,7 +23,6 @@ class PrefService;
 class PrefChangeRegistrar;
 
 namespace base {
-class Clock;
 class DictionaryValue;
 }
 
@@ -61,13 +60,6 @@ class ContentSettingsPref {
 
   void ClearAllContentSettingsRules();
 
-  void UpdateLastUsage(const ContentSettingsPattern& primary_pattern,
-                       const ContentSettingsPattern& secondary_pattern,
-                       base::Clock* clock);
-
-  base::Time GetLastUsage(const ContentSettingsPattern& primary_pattern,
-                          const ContentSettingsPattern& secondary_pattern);
-
   size_t GetNumExceptions();
 
   // Tries to lock |lock_|. If successful, returns true and releases the lock.