Makes -init and -setType: available in CollectionViewItem

ios/chrome/browser/ui/collection_view/cells/collection_view_item.mm

 // 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.
 
 #import "ios/chrome/browser/ui/collection_view/cells/collection_view_item.h"
 
 #import "base/logging.h"
+#import "ios/chrome/browser/ui/collection_view/cells/collection_view_item+Private.h"
 #import "ios/third_party/material_components_ios/src/components/CollectionCells/src/MaterialCollectionCells.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @implementation CollectionViewItem
 
 @synthesize type = _type;
 @synthesize cellClass = _cellClass;
 @synthesize accessibilityIdentifier = _accessibilityIdentifier;
 
 - (instancetype)initWithType:(NSInteger)type {
   if ((self = [super init])) {
     _type = type;
     _cellClass = [MDCCollectionViewCell class];
   }
   return self;
 }
 
 - (instancetype)init {
-  NOTREACHED();
-  return nil;
+  return [self initWithType:0];
 }
 
 - (void)setCellClass:(Class)cellClass {
   DCHECK([cellClass isSubclassOfClass:[MDCCollectionViewCell class]]);
   _cellClass = cellClass;
 }
 
 - (void)configureCell:(MDCCollectionViewCell*)cell {
   DCHECK([cell class] == self.cellClass);
   cell.accessibilityTraits = self.accessibilityTraits;
   cell.accessibilityIdentifier = self.accessibilityIdentifier;
 }
 
 @end
+
+@implementation CollectionViewItem (Private)
+
+- (void)setType:(NSInteger)type {
+  _type = type;

[lpromero, 2017/04/13 21:42:59]

DCHECK type >= kItemTypeEnumStart.

[Moe, 2017/04/14 02:55:38]

This would create a dependency cycle:
//i/c/b/u/collection_view/cells -> //i/c/b/u/collection_view ->
//i/c/b/u/collection_view/cells
I don't think this check is necessary here since it's done in the
CollectionViewModel. 

[lpromero, 2017/04/14 11:37:11]

Acknowledged.

+}
+
+@end