[ios] Plumb SnapshotCache into tab grid.

ios/clean/chrome/browser/ui/tab_collection/tab_collection_view_controller.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_CLEAN_CHROME_BROWSER_UI_TAB_COLLECTION_TAB_COLLECTION_VIEW_CONTROLLER_H_
 #define IOS_CLEAN_CHROME_BROWSER_UI_TAB_COLLECTION_TAB_COLLECTION_VIEW_CONTROLLER_H_
 
 #import <UIKit/UIKit.h>
 
 #import "ios/clean/chrome/browser/ui/tab_collection/tab_collection_consumer.h"
 
+@class SnapshotCache;
+
 // Controller for a scrolling view displaying square cells that represent
 // the user's open tabs.
 @interface TabCollectionViewController
     : UIViewController<TabCollectionConsumer, UICollectionViewDataSource>
 // A collection view of tabs.
 @property(nonatomic, weak, readonly) UICollectionView* tabs;
 // Model for collection view.
 @property(nonatomic, strong, readonly)
     NSMutableArray<TabCollectionItem*>* items;
+// Cache used to retrieve snapshot images for tab cells.
+@property(nonatomic, weak) SnapshotCache* snapshotCache;
 @end
 
 #endif  // IOS_CLEAN_CHROME_BROWSER_UI_TAB_COLLECTION_TAB_COLLECTION_VIEW_CONTROLLER_H_