[NTP Snippets] SnippetsBridge: register as SnippetsObserver only when we get a Java observer

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 16 matching lines @@
   void DiscardSnippet(JNIEnv* env,
                       const base::android::JavaParamRef<jobject>& obj,
                       const base::android::JavaParamRef<jstring>& url);
 
   static bool Register(JNIEnv* env);
 
  private:
   ~NTPSnippetsBridge() override;
 
   // NTPSnippetsServiceObserver overrides
-  void NTPSnippetsServiceLoaded(
-      ntp_snippets::NTPSnippetsService* service) override;
-  void NTPSnippetsServiceShutdown(
-      ntp_snippets::NTPSnippetsService* service) override;
+  void NTPSnippetsServiceLoaded() override;
+  void NTPSnippetsServiceShutdown() override;
 
   ntp_snippets::NTPSnippetsService* ntp_snippets_service_;
 
   // 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_;
 
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsBridge);
 };
 
 #endif  // CHROME_BROWSER_ANDROID_NTP_NTP_SNIPPETS_BRIDGE_H_