Remove EmptyRuleIterators with nullptrs.

components/content_settings/core/browser/content_settings_pref.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_PREF_H_
 #define COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_PREF_H_
 
 #include <stddef.h>
 
 #include <string>
@@ skipping 33 matching lines @@
                               const std::string&)> NotifyObserversCallback;
 
   ContentSettingsPref(ContentSettingsType content_type,
                       PrefService* prefs,
                       PrefChangeRegistrar* registrar,
                       const std::string& pref_name,
                       bool incognito,
                       NotifyObserversCallback notify_callback);
   ~ContentSettingsPref();
 
+  // Returns nullptr to indicate the RuleIterator is empty.
   std::unique_ptr<RuleIterator> GetRuleIterator(
       const ResourceIdentifier& resource_identifier,
       bool incognito) const;
 
   bool SetWebsiteSetting(const ContentSettingsPattern& primary_pattern,
                          const ContentSettingsPattern& secondary_pattern,
                          const ResourceIdentifier& resource_identifier,
                          base::Value* value);
 
   void ClearPref();
@@ skipping 70 matching lines @@
   mutable base::Lock lock_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentSettingsPref);
 };
 
 }  // namespace content_settings
 
 #endif  // COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_PREF_H_