Add Category wrapper for ContentSuggestions on iOS

ios/chrome/browser/ui/content_suggestions/content_suggestions_section_information.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_SUGGESTIONS_SECTION_INFORMATION_H_
+#define IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_SECTION_INFORMATION_H_
+
+#import <Foundation/Foundation.h>
+
+#import "ios/chrome/browser/ui/collection_view/cells/collection_view_item.h"
+
+// Layout for the section and its items.
+typedef NS_ENUM(NSInteger, ContentSuggestionsSectionLayout) {
+  // Follows the card layout.
+  ContentSuggestionsSectionLayoutCard,
+  // No specific layout.
+  ContentSuggestionsSectionLayoutCustom,
+};
+
+// This enum is used for ordering the sections and as ID for the section. Make
+// all sections in the same collection have different ID.
+// When adding a new kind of suggestions, add a new corresponding section.

[stkhapugin, 2017/02/13 15:42:49]

nit: I know it looks obvious, but can you add a comment saying "these values are
never persisted between launches" if this is the case, or otherwise note that
they may be persisted?

[gambard, 2017/02/13 16:28:02]

Done.

+typedef NS_ENUM(NSInteger, ContentSuggestionsSectionID) {
+  ContentSuggestionsSectionBookmarks = 0,
+  ContentSuggestionsSectionArticles = 1,
+
+  // Do not use this. It will trigger a DCHECK.
+  // Do not add value after this one.
+  ContentSuggestionsSectionCount
+};
+
+// Contains the information needed to display the section.
+@interface ContentSuggestionsSectionInformation : NSObject
+
+- (instancetype)initWithID:(ContentSuggestionsSectionID)ID;
+- (instancetype)init NS_UNAVAILABLE;
+
+// Item to display when the section is empty. If nil the section should not be
+// displayed when empty.
+@property(nonatomic, strong) CollectionViewItem* emptyCell;

[stkhapugin, 2017/02/13 15:42:49]

optional: I'm almost certain you will never write into this property, so you
might make it readonly and change designated initializer to
initWithID:emptyCell:. 

[gambard, 2017/02/13 16:28:00]

Done.

+// Layout to display the content of the section.
+@property(nonatomic, assign) ContentSuggestionsSectionLayout layout;

[stkhapugin, 2017/02/13 15:42:49]

Optional: same here, I'm almost sure you'll never write to this, so you can
stick |layout| into designated initialzier and make this readonly. 

[gambard, 2017/02/13 16:28:01]

Done.

+// ID of the section. Used for ordering.
+@property(nonatomic, assign, readonly) ContentSuggestionsSectionID ID;
+// Title for the section.
+@property(nonatomic, copy) NSString* title;

[stkhapugin, 2017/02/13 15:42:49]

Optional: And this one. 

[gambard, 2017/02/13 16:28:01]

Done.

+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_SECTION_INFORMATION_H_