Refactor TabModel to use WebStateList to store WebStates.

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 <utility>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 10 matching lines @@
 #include "components/sessions/ios/ios_live_tab.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #include "ios/chrome/browser/chrome_url_constants.h"
 #import "ios/chrome/browser/chrome_url_util.h"
 #import "ios/chrome/browser/metrics/tab_usage_recorder.h"
 #include "ios/chrome/browser/sessions/ios_chrome_tab_restore_service_factory.h"
 #import "ios/chrome/browser/sessions/session_service.h"
 #import "ios/chrome/browser/sessions/session_window.h"
 #import "ios/chrome/browser/snapshots/snapshot_cache.h"
 #include "ios/chrome/browser/tab_parenting_global_observer.h"
+#import "ios/chrome/browser/tabs/legacy_tab_helper.h"
 #import "ios/chrome/browser/tabs/tab.h"
 #import "ios/chrome/browser/tabs/tab_model_list.h"
 #import "ios/chrome/browser/tabs/tab_model_observers.h"
 #import "ios/chrome/browser/tabs/tab_model_order_controller.h"
 #import "ios/chrome/browser/tabs/tab_model_synced_window_delegate.h"
 #import "ios/chrome/browser/xcallback_parameters.h"
+#import "ios/shared/chrome/browser/tabs/web_state_list.h"
+#import "ios/shared/chrome/browser/tabs/web_state_list_fast_enumeration_helper.h"
+#import "ios/shared/chrome/browser/tabs/web_state_list_observer.h"
 #import "ios/web/navigation/crw_session_certificate_policy_manager.h"
 #import "ios/web/navigation/crw_session_controller.h"
 #include "ios/web/public/browser_state.h"
 #include "ios/web/public/certificate_policy_cache.h"
 #include "ios/web/public/navigation_item.h"
 #import "ios/web/public/navigation_manager.h"
 #include "ios/web/public/web_thread.h"
 #import "ios/web/web_state/ui/crw_web_controller.h"
 #import "ios/web/web_state/web_state_impl.h"
 #include "url/gurl.h"
@@ skipping 25 matching lines @@
   DCHECK_CURRENTLY_ON(web::WebThread::UI);
   // TODO(crbug.com/454984): Remove CRWSessionController usage once certificate
   // policy manager is moved to NavigationManager.
   CRWSessionController* controller = static_cast<web::WebStateImpl*>(web_state)
                                          ->GetNavigationManagerImpl()
                                          .GetSessionController();
   [[controller sessionCertificatePolicyManager]
       updateCertificatePolicyCache:policy_cache];
 }
 
-// Populates the certificate policy cache based on the WebStates of |tab_model|.
+// Populates the certificate policy cache based on the WebStates of
+// |web_state_list|.
 void RestoreCertificatePolicyCacheFromModel(
     const scoped_refptr<web::CertificatePolicyCache>& policy_cache,
-    TabModel* tab_model) {
+    WebStateList* web_state_list) {
   DCHECK_CURRENTLY_ON(web::WebThread::UI);
-  for (Tab* tab in tab_model)
-    UpdateCertificatePolicyCacheFromWebState(policy_cache, tab.webState);
+  for (size_t index = 0; index < web_state_list->count(); ++index) {
+    UpdateCertificatePolicyCacheFromWebState(
+        policy_cache, web_state_list->GetWebStateAt(index));
+  }
 }
 
 // Scrubs the certificate policy cache of all certificates policies except
-// those for the current entries in |tab_model|.
+// those for the current entries in |web_state_list|.
 void CleanCertificatePolicyCache(
     base::CancelableTaskTracker* task_tracker,
     const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
     const scoped_refptr<web::CertificatePolicyCache>& policy_cache,
-    TabModel* tab_model) {
-  DCHECK(tab_model);
+    WebStateList* web_state_list) {
   DCHECK(policy_cache);
+  DCHECK(web_state_list);
   DCHECK_CURRENTLY_ON(web::WebThread::UI);
   task_tracker->PostTaskAndReply(
       task_runner.get(), FROM_HERE,
       base::Bind(&web::CertificatePolicyCache::ClearCertificatePolicies,
                  policy_cache),
       base::Bind(&RestoreCertificatePolicyCacheFromModel, policy_cache,
-                 base::Unretained(tab_model)));
+                 base::Unretained(web_state_list)));
 }
 
 }  // anonymous namespace
 
-@interface TabModel ()<TabUsageRecorderDelegate> {
-  // Array of |Tab| objects.
-  base::scoped_nsobject<NSMutableArray> _tabs;
+@interface TabModel ()<TabUsageRecorderDelegate, WebStateProxyFactory> {
+  // Underlying shared model implementation.
+  WebStateList _webStateList;
+
+  // Helper providing NSFastEnumeration implementation over the WebStateList.
+  base::scoped_nsobject<WebStateListFastEnumerationHelper>
+      _fastEnumerationHelper;
+
+  // Used to keep the Tabs alive while the corresponding WebStates are stored
+  // in the WebStateList (as Tabs currently owns their WebState). Remove once

[rohitrao (ping after 24h), 2017/02/14 14:37:12]

"own"

[sdefresne, 2017/02/14 16:45:46]

Done.

+  // WebState owns the associated Tab.
+  base::scoped_nsobject<NSMutableSet<Tab*>> _tabs;

[rohitrao (ping after 24h), 2017/02/14 14:37:12]

Another naming option is to call this something like _tabRetainer, to make it
less likely that someone will use it accidentally.

[sdefresne, 2017/02/14 16:45:46]

Done.

+
   // Maintains policy for where new tabs go and the selection when a tab
   // is removed.
   base::scoped_nsobject<TabModelOrderController> _orderController;
   // The delegate for sync.
   std::unique_ptr<TabModelSyncedWindowDelegate> _syncedWindowDelegate;
   // Currently selected tab. May be nil.
   base::WeakNSObject<Tab> _currentTab;
 
   // Counters for metrics.
   int _openedTabCount;
@@ skipping 83 matching lines @@
   [super dealloc];
 }
 
 #pragma mark - Public methods
 
 - (Tab*)currentTab {
   return _currentTab.get();
 }
 
 - (void)setCurrentTab:(Tab*)newTab {
-  DCHECK([_tabs containsObject:newTab]);
+  DCHECK_NE([self indexOfTab:newTab], static_cast<NSUInteger>(NSNotFound));
   if (_currentTab != newTab) {
     base::RecordAction(base::UserMetricsAction("MobileTabSwitched"));
     [self updateSnapshotCache:newTab];
   }
   if (_tabUsageRecorder) {
     _tabUsageRecorder->RecordTabSwitched(_currentTab, newTab);
   }
   [self changeSelectedTabFrom:_currentTab to:newTab persistState:YES];
 }
 
 - (TabModelSyncedWindowDelegate*)syncedWindowDelegate {
   return _syncedWindowDelegate.get();
 }
 
 - (TabUsageRecorder*)tabUsageRecorder {
   return _tabUsageRecorder.get();
 }
 
 - (BOOL)isOffTheRecord {
   return _browserState && _browserState->IsOffTheRecord();
 }
 
 - (BOOL)isEmpty {
-  return self.count == 0;
+  return _webStateList.empty();
 }
 
 - (NSUInteger)count {
-  return [_tabs count];
+  return _webStateList.count();
 }
 
 - (instancetype)initWithSessionWindow:(SessionWindowIOS*)window
                        sessionService:(SessionServiceIOS*)service
                          browserState:(ios::ChromeBrowserState*)browserState {
   if ((self = [super init])) {
-    _observers.reset([[TabModelObservers
-        observersWithProtocol:@protocol(TabModelObserver)] retain]);
+    _tabs.reset([[NSMutableSet alloc] init]);
+    _observers.reset([[TabModelObservers observers] retain]);
+
+    _fastEnumerationHelper.reset([[WebStateListFastEnumerationHelper alloc]
+        initWithWebStateList:&_webStateList
+                proxyFactory:self]);
 
     _browserState = browserState;
     DCHECK(_browserState);
 
     // There must be a valid session service defined to consume session windows.
     DCHECK(service);
     _sessionService.reset([service retain]);
 
     // 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.reset(new TabUsageRecorder(self));
     }
     _syncedWindowDelegate.reset(new TabModelSyncedWindowDelegate(self));
 
-    _tabs.reset([[NSMutableArray alloc] init]);
     if (window) {
       DCHECK([_observers empty]);
       // Restore the session and reset the session metrics (as the event have
       // not been generated by the user but by a cold start cycle).
       [self restoreSessionWindow:window persistState:NO];
       [self resetSessionMetrics];
     }
 
     _orderController.reset(
         [[TabModelOrderController alloc] initWithTabModel:self]);
@@ skipping 28 matching lines @@
   return nil;
 }
 
 - (BOOL)restoreSessionWindow:(SessionWindowIOS*)window {
   return [self restoreSessionWindow:window persistState:YES];
 }
 
 - (void)saveSessionImmediately:(BOOL)immediately {
   // Do nothing if there are tabs in the model but no selected tab. This is
   // a transitional state.
-  if ((!_currentTab && [_tabs count]) || !_browserState)
+  if ((!_currentTab && _webStateList.count()) || !_browserState)
     return;
   [_sessionService saveWindow:self.windowForSavingSession
               forBrowserState:_browserState
                   immediately:immediately];
 }
 
 - (Tab*)tabAtIndex:(NSUInteger)index {
-  return [_tabs objectAtIndex:index];
+  web::WebState* webState = _webStateList.GetWebStateAt(index);
+  return LegacyTabHelper::GetTabForWebState(webState);
 }
 
 - (NSUInteger)indexOfTab:(Tab*)tab {
-  return [_tabs indexOfObject:tab];
+  size_t index = _webStateList.GetIndexOfWebState(tab.webState);
+  return index == WebStateList::kInvalidIndex ? NSNotFound : index;
 }
 
 - (Tab*)tabWithWindowName:(NSString*)windowName {
   if (!windowName)
     return nil;
-  for (Tab* tab in _tabs.get()) {
+  for (Tab* tab in self) {
     if ([windowName isEqualToString:tab.windowName]) {
       return tab;
     }
   }
   return nil;
 }
 
 - (Tab*)nextTabWithOpener:(Tab*)tab afterTab:(Tab*)afterTab {
   NSUInteger startIndex = NSNotFound;
   // Start looking after |afterTab|. If it's not found, start looking after
   // |tab|. If it's not found either, bail.
   if (afterTab)
     startIndex = [self indexOfTab:afterTab];
   if (startIndex == NSNotFound)
     startIndex = [self indexOfTab:tab];
   if (startIndex == NSNotFound)
     return nil;
   NSString* parentID = tab.tabId;
-  for (NSUInteger i = startIndex + 1; i < [_tabs count]; ++i) {
-    Tab* current = [_tabs objectAtIndex:i];
+  for (NSUInteger i = startIndex + 1; i < _webStateList.count(); ++i) {
+    Tab* current = [self tabAtIndex:i];
     DCHECK([current navigationManager]);
     CRWSessionController* sessionController =
         [current navigationManager]->GetSessionController();
     if ([sessionController.openerId isEqualToString:parentID])
       return current;
   }
   return nil;
 }
 
 - (Tab*)firstTabWithOpener:(Tab*)tab {
   if (!tab)
     return nil;
   NSUInteger stopIndex = [self indexOfTab:tab];
   if (stopIndex == NSNotFound)
     return nil;
   NSString* parentID = tab.tabId;
   // Match the navigation index as well as the session id, to better match the
   // state of the tab. I.e. two tabs are opened via a link from tab A, and then
   // a new url is loaded into tab A, and more tabs opened from that url, the
   // latter two tabs should not be grouped with the former two. The navigation
   // index is the simplest way to detect navigation changes.
   DCHECK([tab navigationManager]);
   NSInteger parentNavIndex = [tab navigationManager]->GetCurrentItemIndex();
   for (NSUInteger i = 0; i < stopIndex; ++i) {
-    Tab* tabToCheck = [_tabs objectAtIndex:i];
+    Tab* tabToCheck = [self tabAtIndex:i];
     DCHECK([tabToCheck navigationManager]);
     CRWSessionController* sessionController =
         [tabToCheck navigationManager]->GetSessionController();
     if ([sessionController.openerId isEqualToString:parentID] &&
         sessionController.openerNavigationIndex == parentNavIndex) {
       return tabToCheck;
     }
   }
   return nil;
 }
 
 - (Tab*)lastTabWithOpener:(Tab*)tab {
   NSUInteger startIndex = [self indexOfTab:tab];
   if (startIndex == NSNotFound)
     return nil;
   // There is at least one tab in the model, because otherwise the above check
   // would have returned.
   NSString* parentID = tab.tabId;
   DCHECK([tab navigationManager]);
   NSInteger parentNavIndex = [tab navigationManager]->GetCurrentItemIndex();
 
   Tab* match = nil;
   // Find the last tab in the first matching 'group'.  A 'group' is a set of
   // tabs whose opener's id and opener's navigation index match. The navigation
   // index is used in addition to the session id to detect navigations changes
   // within the same session.
-  for (NSUInteger i = startIndex + 1; i < [_tabs count]; ++i) {
-    Tab* tabToCheck = [_tabs objectAtIndex:i];
+  for (NSUInteger i = startIndex + 1; i < _webStateList.count(); ++i) {
+    Tab* tabToCheck = [self tabAtIndex:i];
     DCHECK([tabToCheck navigationManager]);
     CRWSessionController* sessionController =
         [tabToCheck navigationManager]->GetSessionController();
     if ([sessionController.openerId isEqualToString:parentID] &&
         sessionController.openerNavigationIndex == parentNavIndex) {
       match = tabToCheck;
     } else if (match) {
       break;
     }
   }
   return match;
 }
 
 - (Tab*)openerOfTab:(Tab*)tab {
   if (![tab navigationManager])
     return nil;
   NSString* openerId = [tab navigationManager]->GetSessionController().openerId;
   if (!openerId.length)  // Short-circuit if opener is empty.
     return nil;
-  for (Tab* iteratedTab in _tabs.get()) {
+  for (Tab* iteratedTab in self) {
     if ([iteratedTab.tabId isEqualToString:openerId])
       return iteratedTab;
   }
   return nil;
 }
 
 - (Tab*)insertOrUpdateTabWithURL:(const GURL&)URL
                         referrer:(const web::Referrer&)referrer
                       transition:(ui::PageTransition)transition
                       windowName:(NSString*)windowName
@@ skipping 72 matching lines @@
   DCHECK_EQ(webState->GetBrowserState(), _browserState);
   base::scoped_nsobject<Tab> tab(
       [[Tab alloc] initWithWebState:std::move(webState) model:self]);
   [tab webController].webUsageEnabled = webUsageEnabled_;
   [self insertTab:tab atIndex:index];
   return tab;
 }
 
 - (void)insertTab:(Tab*)tab atIndex:(NSUInteger)index {
   DCHECK(tab);
-  DCHECK(index <= [_tabs count]);
+  DCHECK(![_tabs containsObject:tab]);
   [tab fetchFavicon];
-  [_tabs insertObject:tab atIndex:index];
 
+  [_tabs addObject:tab];
+  _webStateList.InsertWebState(index, tab.webState);
   TabParentingGlobalObserver::GetInstance()->OnTabParented(tab.webState);
   [_observers tabModel:self didInsertTab:tab atIndex:index inForeground:NO];
   [_observers tabModelDidChangeTabCount:self];
 
   base::RecordAction(base::UserMetricsAction("MobileNewTabOpened"));
   // Persist the session due to a new tab being inserted. If this is a
   // background tab (will not become active), saving now will capture the
   // state properly. If it does eventually become active, another save will
   // be triggered to properly capture the end result.
   [self saveSessionImmediately:NO];
+
   ++_newTabCount;
 }
 
 - (void)moveTab:(Tab*)tab toIndex:(NSUInteger)toIndex {

[rohitrao (ping after 24h), 2017/02/14 14:37:12]

DCHECK([_tabs containsObject:tab]);

-  NSUInteger fromIndex = [self indexOfTab:tab];
-  DCHECK_NE(NSNotFound, static_cast<NSInteger>(fromIndex));
-  DCHECK_LT(toIndex, self.count);
-  if (fromIndex == NSNotFound || toIndex >= self.count ||
-      fromIndex == toIndex) {
-    return;
-  }
-
-  base::scoped_nsobject<Tab> tabSaver([tab retain]);
-  [_tabs removeObject:tab];
-  [_tabs insertObject:tab atIndex:toIndex];
-
+  size_t fromIndex = _webStateList.GetIndexOfWebState(tab.webState);
+  _webStateList.MoveWebStateAt(fromIndex, toIndex);
   [_observers tabModel:self didMoveTab:tab fromIndex:fromIndex toIndex:toIndex];
 }
 
 - (void)replaceTab:(Tab*)oldTab withTab:(Tab*)newTab {
   NSUInteger index = [self indexOfTab:oldTab];
   DCHECK_NE(NSNotFound, static_cast<NSInteger>(index));
+  DCHECK([_tabs containsObject:oldTab]);
+  DCHECK(![_tabs containsObject:newTab]);
 
   base::scoped_nsobject<Tab> tabSaver([oldTab retain]);
   [newTab fetchFavicon];
-  [_tabs replaceObjectAtIndex:index withObject:newTab];
+  [_tabs removeObject:oldTab];
+  [_tabs addObject:newTab];
   [newTab setParentTabModel:self];
 
+  _webStateList.ReplaceWebStateAt(index, newTab.webState);
   TabParentingGlobalObserver::GetInstance()->OnTabParented(newTab.webState);
   [_observers tabModel:self didReplaceTab:oldTab withTab:newTab atIndex:index];
 
   if (self.currentTab == oldTab)
     [self changeSelectedTabFrom:nil to:newTab persistState:NO];
 
   [oldTab setParentTabModel:nil];
   [oldTab close];
 
   // Record a tab clobber, since swapping tabs bypasses the tab code that would
   // normally log clobbers.
   base::RecordAction(base::UserMetricsAction("MobileTabClobbered"));
 }
 
 - (void)closeTabAtIndex:(NSUInteger)index {
-  DCHECK(index < [_tabs count]);
-  [self closeTab:[_tabs objectAtIndex:index]];
+  DCHECK(index < _webStateList.count());
+  [self closeTab:[self tabAtIndex:index]];
 }
 
 - (void)closeTab:(Tab*)tab {
   // Ensure the tab stays alive long enough for us to send out the
   // notice of its destruction to the delegate.
   [_observers tabModel:self willRemoveTab:tab];
   [tab close];  // Note it is not safe to access the tab after 'close'.
 }
 
 - (void)closeAllTabs {
   // If this changes, _closedTabCount metrics need to be adjusted.
   for (NSInteger i = self.count - 1; i >= 0; --i)
     [self closeTabAtIndex:i];
   [[NSNotificationCenter defaultCenter]
       postNotificationName:kTabModelAllTabsDidCloseNotification
                     object:self];
 }
 
 - (void)haltAllTabs {
-  for (Tab* tab in _tabs.get()) {
+  for (Tab* tab in self) {
     [tab terminateNetworkActivity];
   }
 }
 
 - (void)notifyTabChanged:(Tab*)tab {
   [_observers tabModel:self didChangeTab:tab];
 }
 
 - (void)addObserver:(id<TabModelObserver>)observer {
   [_observers addObserver:observer];
@@ skipping 16 matching lines @@
                               200, 50);
   UMA_HISTOGRAM_CUSTOM_COUNTS("Session.NewTabCounts", _newTabCount, 1, 200, 50);
 }
 
 - (void)notifyTabSnapshotChanged:(Tab*)tab withImage:(UIImage*)image {
   DCHECK([NSThread isMainThread]);
   [_observers tabModel:self didChangeTabSnapshot:tab withImage:image];
 }
 
 - (void)resetAllWebViews {
-  for (Tab* tab in _tabs.get()) {
+  for (Tab* tab in self) {
     [tab.webController reinitializeWebViewAndReload:(tab == _currentTab)];
   }
 }
 
 - (void)setWebUsageEnabled:(BOOL)webUsageEnabled {
   if (webUsageEnabled_ == webUsageEnabled)
     return;
   webUsageEnabled_ = webUsageEnabled;
-  for (Tab* tab in _tabs.get()) {
+  for (Tab* tab in self) {
     tab.webUsageEnabled = webUsageEnabled;
   }
 }
 
 - (void)setPrimary:(BOOL)primary {
   if (_tabUsageRecorder)
     _tabUsageRecorder->RecordPrimaryTabModelChange(primary, _currentTab);
 }
 
 - (NSSet*)currentlyReferencedExternalFiles {
   NSMutableSet* referencedFiles = [NSMutableSet set];
   if (!_browserState)
     return referencedFiles;
   // Check the currently open tabs for external files.
-  for (Tab* tab in _tabs.get()) {
+  for (Tab* tab in self) {
     if (UrlIsExternalFileReference(tab.url)) {
       NSString* fileName = base::SysUTF8ToNSString(tab.url.ExtractFileName());
       [referencedFiles addObject:fileName];
     }
   }
   // Do the same for the recently closed tabs.
   sessions::TabRestoreService* restoreService =
       IOSChromeTabRestoreServiceFactory::GetForBrowserState(_browserState);
   DCHECK(restoreService);
   for (const auto& entry : restoreService->entries()) {
@@ skipping 16 matching lines @@
   [[NSNotificationCenter defaultCenter] removeObserver:self];
   if (_browserState) {
     UnregisterTabModelFromChromeBrowserState(_browserState, self);
   }
   _browserState = nullptr;
 }
 
 // Called when a tab is closing, but before its CRWWebController is destroyed.
 // Equivalent to DetachTabContentsAt() in Chrome's TabStripModel.
 - (void)didCloseTab:(Tab*)closedTab {
-  NSUInteger closedTabIndex = [_tabs indexOfObject:closedTab];
+  NSUInteger closedTabIndex = [self indexOfTab:closedTab];
   DCHECK(closedTab);
   DCHECK(closedTabIndex != NSNotFound);
   // Let the sessions::TabRestoreService know about that new tab.
   sessions::TabRestoreService* restoreService =
       _browserState
           ? IOSChromeTabRestoreServiceFactory::GetForBrowserState(_browserState)
           : nullptr;
   web::NavigationManagerImpl* navigationManager = [closedTab navigationManager];
   DCHECK(navigationManager);
   int itemCount = navigationManager->GetItemCount();
   if (restoreService && (![self isNTPTab:closedTab] || itemCount > 1)) {
     restoreService->CreateHistoricalTab(
         sessions::IOSLiveTab::GetForWebState(closedTab.webState),
         static_cast<int>(closedTabIndex));
   }
   // This needs to be called before the tab is removed from the list.
   Tab* newSelection =
       [_orderController determineNewSelectedTabFromRemovedTab:closedTab];
+
   base::scoped_nsobject<Tab> kungFuDeathGrip([closedTab retain]);
-  [_tabs removeObject:closedTab];
 
   // If closing the current tab, clear |_currentTab| before sending any
   // notification. This avoids various parts of the code getting confused
   // when the current tab isn't in the tab model.
   Tab* savedCurrentTab = _currentTab;
   if (closedTab == _currentTab)
     _currentTab.reset(nil);
 
+  DCHECK([_tabs containsObject:closedTab]);
+  [_tabs removeObject:closedTab];
+
+  _webStateList.RemoveWebStateAt(closedTabIndex);
   [_observers tabModel:self didRemoveTab:closedTab atIndex:closedTabIndex];
   [_observers tabModelDidChangeTabCount:self];
 
   // Current tab has closed, update the selected tab and swap in its
   // contents. There is nothing to do if a non-selected tab is closed as
   // the selection isn't index-based, therefore it hasn't changed.
   // -changeSelectedTabFrom: will persist the state change, so only do it
   // if the selection isn't changing.
   if (closedTab == savedCurrentTab) {
     [self changeSelectedTabFrom:closedTab to:newSelection persistState:NO];
@@ skipping 27 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 [_tabs countByEnumeratingWithState:state objects:objects count:count];
+  return [_fastEnumerationHelper countByEnumeratingWithState:state
+                                                     objects:objects
+                                                       count:count];
 }
 
 #pragma mark - TabUsageRecorderDelegate
 
 - (NSUInteger)liveTabsCount {
   NSUInteger count = 0;
-  NSArray* tabs = _tabs.get();
-  for (Tab* tab in tabs) {
+  for (Tab* tab in self) {
     if ([tab.webController isViewAlive])
       count++;
   }
   return count;
 }
 
+#pragma mark - WebStateProxyFactory
+
+- (id)proxyForWebState:(web::WebState*)webState {

[rohitrao (ping after 24h), 2017/02/14 14:37:12]

What is this for?

+  return LegacyTabHelper::GetTabForWebState(webState);
+}
+
 #pragma mark - Private methods
 
 - (SessionWindowIOS*)windowForSavingSession {
   // Background tabs will already have their state preserved, but not the
   // fg tab. Do it now.
   [_currentTab recordStateInHistory];
 
   // Build the array of sessions. Copy the session objects as the saving will
   // be done on a separate thread.
   // TODO(crbug.com/661986): This could get expensive especially since this
@@ skipping 144 matching lines @@
 
 - (BOOL)restoreSessionWindow:(SessionWindowIOS*)window
                 persistState:(BOOL)persistState {
   DCHECK(_browserState);
   DCHECK(window);
 
   NSArray* sessions = window.sessions;
   if (!sessions.count)
     return NO;
 
-  size_t oldCount = [_tabs count];
+  size_t oldCount = _webStateList.count();
   web::WebState::CreateParams params(_browserState);
   scoped_refptr<web::CertificatePolicyCache> policyCache =
       web::BrowserState::GetCertificatePolicyCache(_browserState);
 
   for (CRWNavigationManagerStorage* session in sessions) {
     std::unique_ptr<web::WebState> webState =
         web::WebState::Create(params, session);
     DCHECK_EQ(webState->GetBrowserState(), _browserState);
-    Tab* tab =
-        [self insertTabWithWebState:std::move(webState) atIndex:[_tabs count]];
+    Tab* tab = [self insertTabWithWebState:std::move(webState)
+                                   atIndex:_webStateList.count()];
     tab.webController.usePlaceholderOverlay = YES;
 
     // Restore the CertificatePolicyCache (note that webState is invalid after
     // passing it via move semantic to -insertTabWithWebState:atIndex:).
     UpdateCertificatePolicyCacheFromWebState(policyCache, tab.webState);
   }
-  DCHECK_GT([_tabs count], oldCount);
+  DCHECK_GT(_webStateList.count(), oldCount);
 
   // Update the selected tab if there was a selected Tab in the saved session.
   if (window.selectedIndex != NSNotFound) {
     NSUInteger selectedIndex = window.selectedIndex + oldCount;
-    DCHECK_LT(selectedIndex, [_tabs count]);
+    DCHECK_LT(selectedIndex, _webStateList.count());
     DCHECK([self tabAtIndex:selectedIndex]);
     [self changeSelectedTabFrom:_currentTab
                              to:[self tabAtIndex:selectedIndex]
                    persistState:persistState];
   }
 
   // If there was only one tab and it was the new tab page, clobber it.
   BOOL closedNTPTab = NO;
   if (oldCount == 1) {
-    Tab* tab = [_tabs objectAtIndex:0];
+    Tab* tab = [self tabAtIndex:0];
     if (tab.url == GURL(kChromeUINewTabURL)) {
       [self closeTab:tab];
       closedNTPTab = YES;
       oldCount = 0;
     }
   }
   if (_tabUsageRecorder) {
-    _tabUsageRecorder->InitialRestoredTabs(
-        _currentTab,
-        [_tabs
-            subarrayWithRange:NSMakeRange(oldCount, [_tabs count] - oldCount)]);
+    NSMutableArray<Tab*>* restoredTabs =
+        [NSMutableArray arrayWithCapacity:_webStateList.count() - oldCount];
+    for (size_t index = oldCount; index < _webStateList.count(); ++index) {
+      [restoredTabs addObject:[self tabAtIndex:index]];
+    }
+    _tabUsageRecorder->InitialRestoredTabs(_currentTab, restoredTabs);
   }
   return closedNTPTab;
 }
 
 #pragma mark - Notification Handlers
 
 // Called when UIApplicationWillResignActiveNotification is received.
 - (void)willResignActive:(NSNotification*)notify {
   if (webUsageEnabled_ && _currentTab) {
     [[SnapshotCache sharedInstance]
         willBeSavedGreyWhenBackgrounding:_currentTab.get().tabId];
   }
 }
 
 // Called when UIApplicationDidEnterBackgroundNotification is received.
 - (void)applicationDidEnterBackground:(NSNotification*)notify {
   if (!_browserState)
     return;
 
   // Evict all the certificate policies except for the current entries of the
   // active sessions.
   CleanCertificatePolicyCache(
       &_clearPoliciesTaskTracker,
       web::WebThread::GetTaskRunnerForThread(web::WebThread::IO),
-      web::BrowserState::GetCertificatePolicyCache(_browserState), self);
+      web::BrowserState::GetCertificatePolicyCache(_browserState),
+      &_webStateList);
 
   if (_tabUsageRecorder)
     _tabUsageRecorder->AppDidEnterBackground();
 
   // Normally, the session is saved after some timer expires but since the app
   // is about to enter the background send YES to save the session immediately.
   [self saveSessionImmediately:YES];
 
   // Write out a grey version of the current website to disk.
   if (webUsageEnabled_ && _currentTab) {
@@ skipping 38 matching lines @@
   web::NavigationManager::WebLoadParams params(URL);
   params.referrer = referrer;
   params.transition_type = ui::PAGE_TRANSITION_TYPED;
   [[tab webController] loadWithParams:params];
   [tab webController].webUsageEnabled = webUsageEnabled_;
   [self insertTab:tab atIndex:index];
   return tab;
 }
 
 @end