[ios clean] Toolbar displays total number of tabs.

ios/clean/chrome/browser/ui/tab_collection/tab_collection_mediator.mm

 // 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.
 
 #import "ios/clean/chrome/browser/ui/tab_collection/tab_collection_mediator.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/scoped_observer.h"
 #include "base/strings/sys_string_conversions.h"
 #import "ios/chrome/browser/web_state_list/web_state_list.h"
@@ skipping 31 matching lines @@
 
 #pragma mark - Public
 
 - (void)disconnect {
   self.webStateList = nullptr;
 }
 
 #pragma mark - Properties
 
 - (void)setWebStateList:(WebStateList*)webStateList {
+  // TODO(crbug.com/727427):Add support for DCHECK(webStateList).
   _scopedWebStateListObserver->RemoveAll();
   _webStateList = webStateList;
   [self populateConsumerItems];
   if (_webStateList) {
     _scopedWebStateListObserver->Add(_webStateList);
   }
 }
 
 - (void)setConsumer:(id<TabCollectionConsumer>)consumer {
   _consumer = consumer;
@@ skipping 75 matching lines @@
 
 - (void)populateConsumerItems {
   if (self.consumer && self.webStateList) {
     [self.consumer populateItems:[self tabCollectionItemsFromWebStateList:
                                            self.webStateList]];
     [self.consumer selectItemAtIndex:self.webStateList->active_index()];
   }
 }
 
 @end