Remove EmptyRuleIterators with nullptrs.

components/content_settings/core/browser/content_settings_rule.h

Index: components/content_settings/core/browser/content_settings_rule.h
diff --git a/components/content_settings/core/browser/content_settings_rule.h b/components/content_settings/core/browser/content_settings_rule.h
index af7b450a8f963c4c34de3fa0220b117243f7923e..8c24e60ccafd20e9bf15250c5ec93ca1b363dbe7 100644
--- a/components/content_settings/core/browser/content_settings_rule.h
+++ b/components/content_settings/core/browser/content_settings_rule.h
@@ -39,13 +39,6 @@ class RuleIterator {
   virtual Rule Next() = 0;
 };
 
-class EmptyRuleIterator : public RuleIterator {
- public:
-  ~EmptyRuleIterator() override;
-  bool HasNext() const override;
-  Rule Next() override;
-};
-
 class ConcatenationIterator : public RuleIterator {
  public:
   // ConcatenationIterator takes ownership of the pointers in the |iterators|