[Sync] Initial implementation of foreign sessions suggestions provider.

components/ntp_snippets/category.h

Index: components/ntp_snippets/category.h
diff --git a/components/ntp_snippets/category.h b/components/ntp_snippets/category.h
index 524986fb3b8e5af8b93a02bc87cf341d80d80a00..eaf74eb2e7ef7ae89b31e30244749acf98e633f1 100644
--- a/components/ntp_snippets/category.h
+++ b/components/ntp_snippets/category.h
@@ -18,6 +18,9 @@ class CategoryFactory;
 // 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,
@@ -31,6 +34,9 @@ enum class KnownCategories {
   // 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,