[NTP Snippets] Add tests for invalid or incomplete json

components/ntp_snippets/ntp_snippets_service.h

 // 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.
 
 #ifndef COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_SERVICE_H_
 #define COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_SERVICE_H_
 
 #include <stddef.h>
 
 #include <set>
@@ skipping 154 matching lines @@
   // The snippets fetcher.
   scoped_ptr<NTPSnippetsFetcher> snippets_fetcher_;
 
   // The subscription to the snippets fetcher.
   scoped_ptr<NTPSnippetsFetcher::SnippetsAvailableCallbackList::Subscription>
       snippets_fetcher_subscription_;
 
   // Timer that calls us back when the next snippet expires.
   base::OneShotTimer expiry_timer_;
 
-  const ParseJSONCallback parse_json_callback_;
+  ParseJSONCallback parse_json_callback_;
 
   base::WeakPtrFactory<NTPSnippetsService> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsService);
 };
 
 class NTPSnippetsServiceObserver {
  public:
   // Sent every time the service loads a new set of data.
   virtual void NTPSnippetsServiceLoaded() = 0;
   // Sent when the service is shutting down.
   virtual void NTPSnippetsServiceShutdown() = 0;
 
  protected:
   virtual ~NTPSnippetsServiceObserver() {}
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_NTP_SNIPPETS_SERVICE_H_