[NTP Snippets] Another round of clang-tidy cleanups

components/ntp_snippets/content_suggestion.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 COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTION_H_
 #define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTION_H_
 
 #include <string>
 
 #include "base/macros.h"
@@ skipping 24 matching lines @@
 
    private:
     Category category_;
     std::string id_within_category_;
 
     // Allow copy and assignment.
   };
 
   // Creates a new ContentSuggestion. The caller must ensure that the |id|
   // passed in here is unique application-wide.
-  ContentSuggestion(ID id, const GURL& url);
+  ContentSuggestion(const ID& id, const GURL& url);
   ContentSuggestion(Category category,
                     const std::string& id_within_category,
                     const GURL& url);
   ContentSuggestion(ContentSuggestion&&);
   ContentSuggestion& operator=(ContentSuggestion&&);
 
   ~ContentSuggestion();
 
   // An ID for identifying the suggestion. The ID is unique application-wide.
   const ID& id() const { return id_; }
@@ skipping 43 matching lines @@
   GURL amp_url_;
   base::string16 title_;
   base::string16 snippet_text_;
   base::Time publish_date_;
   base::string16 publisher_name_;
   float score_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentSuggestion);
 };
 
-std::ostream& operator<<(std::ostream& os, ContentSuggestion::ID id);
+std::ostream& operator<<(std::ostream& os, const ContentSuggestion::ID& id);
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTION_H_