[NTP Snippets] Don't reschedule background fetching on every startup

components/ntp_snippets/pref_names.h

Index: components/ntp_snippets/pref_names.h
diff --git a/components/ntp_snippets/pref_names.h b/components/ntp_snippets/pref_names.h
index 04c7771f488d37831b2bb25ad045c5246f346fe5..4b2a147311adcb65d5dd0cc83ec7ba000a670289 100644
--- a/components/ntp_snippets/pref_names.h
+++ b/components/ntp_snippets/pref_names.h
@@ -12,6 +12,13 @@ extern const char kEnableSnippets[];
 
 extern const char kSnippetHosts[];
 
+// The pref name for the currently-scheduled background fetching interval when
+// there is WiFi connectivity.
+extern const char kSnippetBackgroundFetchingIntervalWifi[];
+// The pref name for the currently-scheduled background fetching interval when
+// there is no WiFi connectivity.
+extern const char kSnippetBackgroundFetchingIntervalFallback[];
+
 // The pref name for today's count of NTPSnippetsFetcher requests, so far.
 extern const char kSnippetFetcherRequestCount[];
 // The pref name for today's count of NTPSnippetsFetcher interactive requests.