Add ClearHistory() to ContentSuggestionsService and its providers

components/ntp_snippets/ntp_snippets_service.cc

Index: components/ntp_snippets/ntp_snippets_service.cc
diff --git a/components/ntp_snippets/ntp_snippets_service.cc b/components/ntp_snippets/ntp_snippets_service.cc
index 99546b7f2e9ad352b9b6e6c091d5804633cb1c11..753389756378f4081640ff42f04dd8e7b82c8e6a 100644
--- a/components/ntp_snippets/ntp_snippets_service.cc
+++ b/components/ntp_snippets/ntp_snippets_service.cc
@@ -335,6 +335,10 @@ void NTPSnippetsService::FetchSuggestionImage(
                  base::Unretained(this), callback, snippet_id));
 }
 
+void NTPSnippetsService::ClearHistory(base::Time begin, base::Time end) {
+  // TODO(vitaliii): Implement. See crbug.com/641321.
+}
+
 void NTPSnippetsService::ClearCachedSuggestions(Category category) {
   DCHECK_EQ(category, provided_category_);
   if (!initialized())