[NTP Snippets] Clean up NTPSnippetsServiceTests

components/ntp_snippets/ntp_snippet.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_SNIPPET_H_
 #define COMPONENTS_NTP_SNIPPETS_NTP_SNIPPET_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 61 matching lines @@
     publish_date_ = publish_date;
   }
 
   // After this expiration date this snippet should no longer be presented to
   // the user.
   const base::Time& expiry_date() const { return expiry_date_; }
   void set_expiry_date(const base::Time& expiry_date) {
     expiry_date_ = expiry_date;
   }
 
+  // Public for testing.
+  static base::Time TimeFromJsonString(const std::string& timestamp_str);
+  static std::string TimeToJsonString(const base::Time& time);
+
  private:
   const GURL url_;
   std::string site_title_;
   std::string title_;
   GURL favicon_url_;
   GURL salient_image_url_;
   std::string snippet_;
   base::Time publish_date_;
   base::Time expiry_date_;
 
   DISALLOW_COPY_AND_ASSIGN(NTPSnippet);
 };
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_NTP_SNIPPET_H_