[NTP Snippets] Clear the snippets when the user signs out

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 02524508ceca77bf9620436e54bc6604c47ab25e..555e101213efd53b78add33ac071a137b1e92755 100644
--- a/components/ntp_snippets/ntp_snippets_service.cc
+++ b/components/ntp_snippets/ntp_snippets_service.cc
@@ -331,6 +331,11 @@ void NTPSnippetsService::OnSuggestionsChanged(
   StoreSnippetsToPrefs();
   StoreSnippetHostsToPrefs(hosts);
 
+  if (hosts.empty()) {

[Marc Treib, 2016/05/17 14:57:17]

Post-commit drive-by comment: After https://codereview.chromium.org/1922083004/
and https://codereview.chromium.org/1974483002/, we now support fetching without
host restrictions, so this might not be the best place to send the "cleared"
event.
(Relatedly, this method is also broken now, since it filters by hosts even if
host restriction is turned off.)

+    FOR_EACH_OBSERVER(NTPSnippetsServiceObserver, observers_,
+                      NTPSnippetsServiceCleared());
+  }
+
   FOR_EACH_OBSERVER(NTPSnippetsServiceObserver, observers_,
                     NTPSnippetsServiceLoaded());