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.

[stkhapugin, 2017/02/13 12:19:18]

Is it "layout for the section" (= the way this section is laid out) or "layout
for items of a section"?

[gambard, 2017/02/13 14:51:41]

Done.

+typedef NS_ENUM(NSInteger, ContentSuggestionsSectionLayout) {
+  // No specific layout.

[stkhapugin, 2017/02/13 12:19:18]

Optional: Does this match some other enum? Somehow, I expect "custom" layout to
be the last in the list, as it is custom since it doesn't match any other
category, so logically I'd expect to see all previous categories before this
one. 

[gambard, 2017/02/13 14:51:41]

Not really. In the current implementation card = MDCCollectionViewCellStyleCard

+  ContentSuggestionsSectionLayoutCustom,
+  // Follows the card layout.
+  ContentSuggestionsSectionLayoutCard
+};
+
+// 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.
+typedef NS_ENUM(NSInteger, ContentSuggestionsSectionID) {
+  ContentSuggestionsSectionBookmarks = 0,
+  ContentSuggestionsSectionArticles = 1,
+
+  // Do not use this. It will trigger a DCHECK.
+  ContentSuggestionsSectionNotImplemented

[stkhapugin, 2017/02/13 12:19:18]

nit: make this "ContentSuggestionsSectionCount" and replace DCHECK in init from 

DCHECK(ID!=ContentSuggestionsSectionNotImplemented);

to:

DCHECK(ID < ContentSuggestionsSectionCount);

[gambard, 2017/02/13 14:51:41]

Done.

+};
+
+// Contains the information needed to display the section.
+@interface ContentSuggestionsSectionInformation : NSObject
+
+- (instancetype)initWithID:(ContentSuggestionsSectionID)ID;
+- (instancetype)init NS_UNAVAILABLE;
+
+// If this not nil, the section is displaying this cell when it is empty.

[lpromero, 2017/02/13 12:34:55]

"If this is not nil"

[gambard, 2017/02/13 14:51:41]

Done.

+// If it is nil, the section is not displayed when empty.

[lpromero, 2017/02/13 12:34:55]

No action needed: Technically, these comments are not related to this object but
its client, right? For example, this behavior can't be unit tested with this
class alone.

[gambard, 2017/02/13 14:51:41]

I rewrote the comment.

+@property(nonatomic, strong) CollectionViewItem* emptyCell;
+// Layout to display the content of the section.
+@property(nonatomic, assign) ContentSuggestionsSectionLayout layout;
+// ID of the section. Used for ordering.
+@property(nonatomic, assign, readonly) ContentSuggestionsSectionID ID;
+// Title for the section.
+@property(nonatomic, copy) NSString* title;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_SECTION_INFORMATION_H_