[NTP Snippets] Introduce ContentSuggestion::ID

components/ntp_snippets/mock_content_suggestions_provider_observer.h

Index: components/ntp_snippets/mock_content_suggestions_provider_observer.h
diff --git a/components/ntp_snippets/mock_content_suggestions_provider_observer.h b/components/ntp_snippets/mock_content_suggestions_provider_observer.h
index 01e273de249d2089a9839f11658805c3cea5b9ac..12bb1fdc55b5271cd364b92158ded286d7f5a945 100644
--- a/components/ntp_snippets/mock_content_suggestions_provider_observer.h
+++ b/components/ntp_snippets/mock_content_suggestions_provider_observer.h
@@ -37,10 +37,9 @@ class MockContentSuggestionsProviderObserver
                void(ContentSuggestionsProvider* provider,
                     Category category,
                     CategoryStatus new_status));
-  MOCK_METHOD3(OnSuggestionInvalidated,
+  MOCK_METHOD2(OnSuggestionInvalidated,
                void(ContentSuggestionsProvider* provider,
-                    Category category,
-                    const std::string& suggestion_id));
+                    const ContentSuggestion::ID& suggestion_id));
 };
 
 }  // namespace ntp_snippets