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

components/ntp_snippets/ntp_snippets_service.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/ntp_snippets/ntp_snippets_service.h"
 
 #include <algorithm>
 #include <iterator>
 #include <utility>
 
@@ skipping 313 matching lines @@
   snippets_.erase(
       std::remove_if(snippets_.begin(), snippets_.end(),
                      [&hosts](const std::unique_ptr<NTPSnippet>& snippet) {
                        return !hosts.count(snippet->best_source().url.host());
                      }),
       snippets_.end());
 
   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());
 
   FetchSnippetsFromHosts(hosts);
 }
 
 void NTPSnippetsService::OnFetchFinished(
     NTPSnippetsFetcher::OptionalSnippets snippets) {
   if (snippets) {
     // Sparse histogram used because the number of snippets is small (bound by
@@ skipping 149 matching lines @@
     if (snippet->expiry_date() < next_expiry)
       next_expiry = snippet->expiry_date();
   }
   DCHECK_GT(next_expiry, expiry);
   expiry_timer_.Start(FROM_HERE, next_expiry - expiry,
                       base::Bind(&NTPSnippetsService::LoadingSnippetsFinished,
                                  base::Unretained(this)));
 }
 
 }  // namespace ntp_snippets