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

chrome/browser/android/ntp/ntp_snippets_bridge.h

 // Copyright 2016 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.
 
 #ifndef CHROME_BROWSER_ANDROID_NTP_NTP_SNIPPETS_BRIDGE_H_
 #define CHROME_BROWSER_ANDROID_NTP_NTP_SNIPPETS_BRIDGE_H_
 
 #include <jni.h>
 
 #include "base/android/scoped_java_ref.h"
@@ skipping 34 matching lines @@
                       const base::android::JavaParamRef<jstring>& jurl);
 
   static bool Register(JNIEnv* env);
 
  private:
   ~NTPSnippetsBridge() override;
 
   // NTPSnippetsServiceObserver overrides
   void NTPSnippetsServiceLoaded() override;
   void NTPSnippetsServiceShutdown() override;
+  void NTPSnippetsServiceCleared() override;
 
   void OnImageFetched(base::android::ScopedJavaGlobalRef<jobject> callback,
                       const std::string& snippet_id,
                       const SkBitmap* bitmap);
 
   ntp_snippets::NTPSnippetsService* ntp_snippets_service_;
   history::HistoryService* history_service_;
   base::CancelableTaskTracker tracker_;
 
   // Used to notify the Java side when new snippets have been fetched.
   base::android::ScopedJavaGlobalRef<jobject> observer_;
   ScopedObserver<ntp_snippets::NTPSnippetsService,
                  ntp_snippets::NTPSnippetsServiceObserver>
       snippet_service_observer_;
 
   base::WeakPtrFactory<NTPSnippetsBridge> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsBridge);
 };
 
 #endif  // CHROME_BROWSER_ANDROID_NTP_NTP_SNIPPETS_BRIDGE_H_