[ios] Fix WebStateListFastEnumerationHelper observer unregistration.

ios/chrome/browser/tabs/tab_model.mm

 // Copyright 2012 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/tabs/tab_model.h"
 
 #include <cstdint>
 #include <utility>
 #include <vector>
 
@@ skipping 120 matching lines @@
 @end
 
 @interface TabModel ()<TabUsageRecorderDelegate> {
   // Delegate for the WebStateList.
   std::unique_ptr<WebStateListDelegate> _webStateListDelegate;
 
   // Underlying shared model implementation.
   std::unique_ptr<WebStateList> _webStateList;
 
   // Helper providing NSFastEnumeration implementation over the WebStateList.
-  base::scoped_nsobject<WebStateListFastEnumerationHelper>
-      _fastEnumerationHelper;
+  std::unique_ptr<WebStateListFastEnumerationHelper> _fastEnumerationHelper;
 
   // WebStateListObservers reacting to modifications of the model (may send
   // notification, translate and forward events, update metrics, ...).
   std::vector<std::unique_ptr<WebStateListObserver>> _webStateListObservers;
 
   // Strong references to id<WebStateListObserving> wrapped by non-owning
   // WebStateListObserverBridges.
   base::scoped_nsobject<NSArray<id<WebStateListObserving>>>
       _retainedWebStateListObservers;
 
@@ skipping 115 matching lines @@
 - (instancetype)initWithSessionWindow:(SessionWindowIOS*)window
                        sessionService:(SessionServiceIOS*)service
                          browserState:(ios::ChromeBrowserState*)browserState {
   if ((self = [super init])) {
     _observers.reset([[TabModelObservers observers] retain]);
 
     _webStateListDelegate =
         base::MakeUnique<TabModelWebStateListDelegate>(self);
     _webStateList = base::MakeUnique<WebStateList>(_webStateListDelegate.get());
 
-    _fastEnumerationHelper.reset([[WebStateListFastEnumerationHelper alloc]
-        initWithWebStateList:_webStateList.get()
-                proxyFactory:[[TabModelWebStateProxyFactory alloc] init]]);
+    _fastEnumerationHelper =
+        base::MakeUnique<WebStateListFastEnumerationHelper>(
+            _webStateList.get(), [[TabModelWebStateProxyFactory alloc] init]);
 
     _browserState = browserState;
     DCHECK(_browserState);
 
     // Normal browser states are the only ones to get tab restore. Tab sync
     // handles incognito browser states by filtering on profile, so it's
     // important to the backend code to always have a sync window delegate.
     if (!_browserState->IsOffTheRecord()) {
       // Set up the usage recorder before tabs are created.
       _tabUsageRecorder = base::MakeUnique<TabUsageRecorder>(self);
@@ skipping 374 matching lines @@
 
   int tabCount = static_cast<int>(self.count);
   UMA_HISTOGRAM_CUSTOM_COUNTS("Tabs.TabCountPerLoad", tabCount, 1, 200, 50);
 }
 
 #pragma mark - NSFastEnumeration
 
 - (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState*)state
                                   objects:(id*)objects
                                     count:(NSUInteger)count {
-  return [_fastEnumerationHelper countByEnumeratingWithState:state
-                                                     objects:objects
-                                                       count:count];
+  return [_fastEnumerationHelper->GetFastEnumeration()
+      countByEnumeratingWithState:state
+                          objects:objects
+                            count:count];
 }
 
 #pragma mark - TabUsageRecorderDelegate
 
 - (NSUInteger)liveTabsCount {
   NSUInteger count = 0;
   for (Tab* tab in self) {
     if ([tab.webController isViewAlive])
       count++;
   }
@@ skipping 133 matching lines @@
 }
 
 // Called when UIApplicationWillEnterForegroundNotification is received.
 - (void)applicationWillEnterForeground:(NSNotification*)notify {
   if (_tabUsageRecorder) {
     _tabUsageRecorder->AppWillEnterForeground();
   }
 }
 
 @end