[Sync] Initial implementation of foreign sessions suggestions provider.

components/ntp_snippets/category.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_CATEGORY_H_
 #define COMPONENTS_NTP_SNIPPETS_CATEGORY_H_
 
 #include <ostream>
 
 namespace ntp_snippets {
 
 class CategoryFactory;
 
 // These are the categories that the client knows about.
 // The values before LOCAL_CATEGORIES_COUNT are the categories that are provided
 // locally on the device. Categories provided by the server (IDs strictly larger
 // than REMOTE_CATEGORIES_OFFSET) only need to be hard-coded here if they need
 // to be recognized by the client implementation.
 // On Android builds, a Java counterpart will be generated for this enum.
 // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.chrome.browser.ntp.snippets
+//
+// Note: When adding new categories, one should also consider adding a category
+// to histogram suffix mapping to content_suggestions_metrics.cc.

[Marc Treib, 2016/09/16 12:26:48]

Thanks! This warning should soon not be needed anymore though, see
https://codereview.chromium.org/2337103003/

[skym, 2016/09/16 18:18:47]

Sweet, removed!

 enum class KnownCategories {
   // Pages recently downloaded during normal navigation.
   RECENT_TABS,
 
   // Pages downloaded by the user for offline consumption.
   DOWNLOADS,
 
   // Recently used bookmarks.
   BOOKMARKS,
 
   // Physical Web page available in the vicinity.
   PHYSICAL_WEB_PAGES,
 
+  // Pages recently browsed to on other devices.
+  FOREIGN_TABS,
+
   // Follows the last local category.
   LOCAL_CATEGORIES_COUNT,
 
   REMOTE_CATEGORIES_OFFSET = 10000,
 
   // Articles for you.
   ARTICLES,
 };
 
 // A category groups ContentSuggestions which belong together. Use the
@@ skipping 29 matching lines @@
 
 struct Category::CompareByID {
   bool operator()(const Category& left, const Category& right) const;
 };
 
 std::ostream& operator<<(std::ostream& os, const Category& obj);
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CATEGORY_H_