Change NTPSnippetsService to implement ContentSuggestionsProvider

components/ntp_snippets/content_suggestions_category_status.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_SUGGESTIONS_CATEGORY_STATUS_H_
 #define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_CATEGORY_STATUS_H_
 
 namespace ntp_snippets {
 
 // Represents the status of a category of content suggestions.
 // On Android builds, a Java counterpart will be generated for this enum.
 // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.chrome.browser.ntp.snippets
 enum class ContentSuggestionsCategoryStatus {
+  // The provider is still initializing and it is not yet determined whether
+  // content suggestions will be available or not.
+  INITIALIZING,
+
   // Content suggestions are available (though the list of available suggestions
   // may be empty simply because there are no reasonable suggestions to be made
   // at the moment).
   AVAILABLE,
   // Content suggestions are provided but not yet loaded.
   AVAILABLE_LOADING,
 
   // There is no provider that provides suggestions for this category.
   NOT_PROVIDED,
   // The entire content suggestions feature has explicitly been disabled as part
   // of the service configuration.
   ALL_SUGGESTIONS_EXPLICITLY_DISABLED,
   // Content suggestions from a specific category have been disabled as part of
   // the service configuration.
   CATEGORY_EXPLICITLY_DISABLED,
 
   // Content suggestions are not available because the user is not signed in.
   SIGNED_OUT,
   // Content suggestions are not available because sync is disabled.
   SYNC_DISABLED,
   // Content suggestions are not available because passphrase encryption is
   // enabled (and it should be disabled).
   PASSPHRASE_ENCRYPTION_ENABLED,
   // Content suggestions are not available because history sync is disabled.
   HISTORY_SYNC_DISABLED,
-  // Content suggestions are not available because the history sync service is
-  // not yet completely initialized and its status is unknown.
-  HISTORY_SYNC_STATE_UNKNOWN
+
+  // Content suggestions are not available because an error occured when loading
+  // or updating them.
+  ERROR
 };
 
 // Determines whether the given status is one of the AVAILABLE statuses.
 bool IsContentSuggestionsCategoryStatusAvailable(
     ContentSuggestionsCategoryStatus status);
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_CATEGORY_STATUS_H_