Add a message to empty ContentSuggestions sections

ios/chrome/browser/ui/content_suggestions/content_suggestion.h

 // Copyright 2017 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 IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTION_H_
 #define IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTION_H_
 
 #import <UIKit/UIKit.h>
 
 #import "ios/chrome/browser/ui/content_suggestions/identifier/content_suggestion_identifier.h"
 
 namespace base {
 class Time;
 }
 
 class GURL;
 
 // Enum defining the type of a ContentSuggestions.
 typedef NS_ENUM(NSInteger, ContentSuggestionType) {
+  // Use this type to pass information about an empty section. Suggestion of
+  // this type are empty and should not be displayed. The informations to be
+  // displayed are contained in the SectionInfo.
+  ContentSuggestionTypeEmpty,
   ContentSuggestionTypeArticle
 };
 
 // Data for a suggestions item, compatible with Objective-C. Mostly acts as a
 // wrapper for ntp_snippets::ContentSuggestion.
 @interface ContentSuggestion : NSObject<ContentSuggestionIdentification>
 
 // Title of the suggestion.
 @property(nonatomic, copy, nullable) NSString* title;
 // Text for the suggestion.
 @property(nonatomic, copy, nullable) NSString* text;
 // URL associated with the suggestion.
 @property(nonatomic, assign) GURL url;
 // The name of the publisher.
 @property(nonatomic, copy, nullable) NSString* publisher;
 // The date of publication.
 @property(nonatomic, assign) base::Time publishDate;
 
 @property(nonatomic, assign) ContentSuggestionType type;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTION_H_