[NTP Snippets] Introduce ContentSuggestion::ID

components/ntp_snippets/content_suggestion.cc

 // 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.
 
 #include "components/ntp_snippets/content_suggestion.h"
 
 namespace ntp_snippets {
 
-ContentSuggestion::ContentSuggestion(const std::string& id, const GURL& url)
+bool ContentSuggestion::ID::operator==(const ID& rhs) const {
+  return category_ == rhs.category_ &&
+         id_within_category_ == rhs.id_within_category_;
+}
+
+bool ContentSuggestion::ID::operator!=(const ID& rhs) const {
+  return !(*this == rhs);
+}
+
+ContentSuggestion::ContentSuggestion(ID id, const GURL& url)
     : id_(id), url_(url), score_(0) {}
 
+ContentSuggestion::ContentSuggestion(Category category,
+                                     const std::string& id_within_category,
+                                     const GURL& url)
+    : id_(category, id_within_category), url_(url), score_(0) {}
+
 ContentSuggestion::ContentSuggestion(ContentSuggestion&&) = default;
 
 ContentSuggestion& ContentSuggestion::operator=(ContentSuggestion&&) = default;
 
 ContentSuggestion::~ContentSuggestion() = default;
 
+std::ostream& operator<<(std::ostream& os, ContentSuggestion::ID id) {
+  os << id.category() << "|" << id.id_within_category();
+  return os;
+}
+
 }  // namespace ntp_snippets