Upstream Chrome on iOS source code [2/11].

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 <list>
+#include <utility>
+#include <vector>
+
+#include "base/bind.h"
+#import "base/ios/crb_protocol_observers.h"
+#include "base/logging.h"
+#import "base/mac/scoped_nsobject.h"
+#include "base/metrics/histogram.h"
+#include "base/metrics/user_metrics.h"
+#include "base/metrics/user_metrics_action.h"
+#include "base/strings/sys_string_conversions.h"
+#include "base/supports_user_data.h"
+#include "components/sessions/core/serialized_navigation_entry.h"
+#include "components/sessions/core/session_id.h"
+#include "components/sessions/core/tab_restore_service.h"
+#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/tab.h"
+#import "ios/chrome/browser/tabs/tab_model_observer.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/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"
+
+NSString* const kTabModelTabWillStartLoadingNotification =
+    @"kTabModelTabWillStartLoadingNotification";
+NSString* const kTabModelUserNavigatedNotification = @"kTabModelUserNavigation";
+NSString* const kTabModelTabDidStartLoadingNotification =
+    @"kTabModelTabDidStartLoadingNotification";
+NSString* const kTabModelTabDidFinishLoadingNotification =
+    @"kTabModelTabDidFinishLoadingNotification";
+NSString* const kTabModelAllTabsDidCloseNotification =
+    @"kTabModelAllTabsDidCloseNotification";
+NSString* const kTabModelTabDeselectedNotification =
+    @"kTabModelTabDeselectedNotification";
+NSString* const kTabModelNewTabWillOpenNotification =
+    @"kTabModelNewTabWillOpenNotification";
+NSString* const kTabModelTabKey = @"tab";
+NSString* const kTabModelPageLoadSuccess = @"pageLoadSuccess";
+NSString* const kTabModelOpenInBackgroundKey = @"shouldOpenInBackground";
+
+namespace {
+
+// Updates CRWSessionCertificatePolicyManager's certificate policy cache.
+void UpdateCertificatePolicyCacheFromWebState(web::WebStateImpl* webState) {
+  DCHECK([NSThread isMainThread]);
+  DCHECK(webState);
+  scoped_refptr<web::CertificatePolicyCache> policy_cache =
+      web::BrowserState::GetCertificatePolicyCache(webState->GetBrowserState());
+  CRWSessionController* controller =
+      webState->GetNavigationManagerImpl().GetSessionController();
+  [[controller sessionCertificatePolicyManager]
+      updateCertificatePolicyCache:policy_cache];
+}
+
+// Populates the certificate policy cache based on the current entries of the
+// given tabs.
+void RestoreCertificatePolicyCacheFromTabs(NSArray* tabs) {
+  DCHECK([NSThread isMainThread]);
+  for (Tab* tab in tabs) {
+    UpdateCertificatePolicyCacheFromWebState(tab.webStateImpl);
+  }
+}
+
+// Scrubs the certificate policy cache of all the certificate policies except
+// those for the current entries of the given tabs.
+void CleanCertificatePolicyCache(
+    scoped_refptr<web::CertificatePolicyCache> policy_cache,
+    NSArray* tabs) {
+  DCHECK_CURRENTLY_ON(web::WebThread::IO);
+  DCHECK(policy_cache);
+  policy_cache->ClearCertificatePolicies();
+  web::WebThread::PostTask(
+      web::WebThread::UI, FROM_HERE,
+      base::Bind(&RestoreCertificatePolicyCacheFromTabs, tabs));
+}
+
+// Wrapper class to attach a TabModel to a base::SupportsUserData object, such
+// as an ios::ChromeBrowserState. This wrapper retains the TabModel it wraps, so
+// any base::SupportsUserData object storing such a wrapper has ownership of the
+// TabModel.
+class TabModelHandle : public base::SupportsUserData::Data {
+ public:
+  explicit TabModelHandle(TabModel* model) : tab_model_([model retain]) {}
+  ~TabModelHandle() override {}
+  TabModel* tab_model() { return tab_model_; }
+
+ private:
+  base::scoped_nsobject<TabModel> tab_model_;
+};
+
+// Key for storing a TabModelHandle in a ChromeBrowserState.
+const char kTabModelKeyName[] = "tab_model";
+
+}  // anonymous namespace
+
+@interface TabModelObservers : CRBProtocolObservers<TabModelObserver>
+@end
+@implementation TabModelObservers
+@end
+
+@interface TabModel ()<TabUsageRecorderDelegate> {
+  // Array of |Tab| objects.
+  base::scoped_nsobject<NSMutableArray> _tabs;
+  // 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;
+  int _closedTabCount;
+  int _newTabCount;
+
+  // Backs up property with the same name.
+  std::unique_ptr<TabUsageRecorder> _tabUsageRecorder;
+  // Backs up property with the same name.
+  const SessionID _sessionID;
+  // Saves session's state.
+  base::scoped_nsobject<SessionServiceIOS> _sessionService;
+  // List of TabModelObservers.
+  base::scoped_nsobject<TabModelObservers> _observers;
+}
+
+// Session window for the contents of the tab model.
+@property(nonatomic, readonly) SessionWindowIOS* windowForSavingSession;
+
+// Returns YES if tab URL host indicates that tab is an NTP tab.
+- (BOOL)isNTPTab:(Tab*)tab;
+
+// Opens a tab at the specified URL and registers its JS-supplied window name if
+// appropriate. For certain transition types, will consult the order controller
+// and thus may only use |index| as a hint. |parentTab| may be nil if there
+// is no parent associated with this new tab, as may |windowName| if not
+// applicable. |openedByDOM| is YES if the page was opened by DOM.
+// The |index| parameter can be set to
+// TabModelConstants::kTabPositionAutomatically if the caller doesn't have a
+// preference for the position of the tab.
+- (Tab*)insertTabWithLoadParams:
+            (const web::NavigationManager::WebLoadParams&)params
+                     windowName:(NSString*)windowName
+                         opener:(Tab*)parentTab
+                    openedByDOM:(BOOL)openedByDOM
+                        atIndex:(NSUInteger)index
+                   inBackground:(BOOL)inBackground;
+// Call to switch the selected tab. Broadcasts about the change in selection.
+// It's ok for |newTab| to be nil in case the last tab is going away. In that
+// case, the "tab deselected" notification gets sent, but no corresponding
+// "tab selected" notification is sent. |persist| indicates whether or not
+// the tab's state should be persisted in history upon switching.
+- (void)changeSelectedTabFrom:(Tab*)oldTab
+                           to:(Tab*)newTab
+                 persistState:(BOOL)persist;
+// Tells the snapshot cache the adjacent tab session ids.
+- (void)updateSnapshotCache:(Tab*)tab;
+// Helper method that posts a notification with the given name with |tab|
+// in the userInfo dictionary under the kTabModelTabKey.
+- (void)postNotificationName:(NSString*)notificationName withTab:(Tab*)tab;
+@end
+
+@implementation TabModel
+
+@synthesize browserState = _browserState;
+@synthesize sessionID = _sessionID;
+@synthesize webUsageEnabled = webUsageEnabled_;
+
+#pragma mark - Overriden
+
+- (void)dealloc {
+  DCHECK([_observers empty]);
+  // browserStateDestroyed should always have been called before destruction.
+  DCHECK(!_browserState);
+
+  [[NSNotificationCenter defaultCenter] removeObserver:self];
+  // Make sure the tabs do clean after themselves. It is important for
+  // removeObserver: to be called first otherwise a lot of unecessary work will
+  // happen on -closeAllTabs.
+  [self closeAllTabs];
+
+  [super dealloc];
+}
+
+#pragma mark - Public methods
+
+- (Tab*)currentTab {
+  return _currentTab.get();
+}
+
+- (void)setCurrentTab:(Tab*)newTab {
+  DCHECK([_tabs containsObject:newTab]);
+  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;
+}
+
+- (NSUInteger)count {
+  return [_tabs count];
+}
+
++ (instancetype)tabModelForBrowserState:(ios::ChromeBrowserState*)browserState {
+  if (!browserState)
+    return nil;
+  TabModelHandle* handle =
+      static_cast<TabModelHandle*>(browserState->GetUserData(kTabModelKeyName));
+  return handle ? handle->tab_model() : nil;
+}
+
+- (instancetype)initWithSessionWindow:(SessionWindowIOS*)window
+                       sessionService:(SessionServiceIOS*)service
+                         browserState:(ios::ChromeBrowserState*)browserState {
+  if ((self = [super init])) {
+    _observers.reset([[TabModelObservers
+        observersWithProtocol:@protocol(TabModelObserver)] retain]);
+
+    _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]);
+    NSNotificationCenter* defaultCenter = [NSNotificationCenter defaultCenter];
+    if (window) {
+      while (window.unclaimedSessions) {
+        std::unique_ptr<web::WebStateImpl> webState = [window nextSession];
+        DCHECK_EQ(webState->GetBrowserState(), _browserState);
+        // Restore the CertificatePolicyCache.
+        UpdateCertificatePolicyCacheFromWebState(webState.get());
+        // Create a new tab for each entry in the window. Don't send delegate
+        // notifications for each restored tab, only when all done.
+        base::scoped_nsobject<Tab> tab(
+            [[Tab alloc] initWithWebState:std::move(webState) model:self]);
+        [tab webController].usePlaceholderOverlay = YES;
+        [tab fetchFavicon];
+        [_tabs addObject:tab];
+
+        TabParentingGlobalObserver::GetInstance()->OnTabParented(
+            [tab webStateImpl]);
+      }
+      if ([_tabs count]) {
+        DCHECK(window.selectedIndex < [_tabs count]);
+        _currentTab.reset([self tabAtIndex:window.selectedIndex]);
+        DCHECK(_currentTab);
+        if (_tabUsageRecorder)
+          _tabUsageRecorder->InitialRestoredTabs(_currentTab, _tabs);
+        // Perform initializations for affiliated objects which update the
+        // session information related to the current tab.
+        [_currentTab updateLastVisitedTimestamp];
+        [self saveSessionImmediately:NO];
+      }
+    }
+
+    _orderController.reset(
+        [[TabModelOrderController alloc] initWithTabModel:self]);
+    // Register for resign active notification.
+    [defaultCenter addObserver:self
+                      selector:@selector(willResignActive:)
+                          name:UIApplicationWillResignActiveNotification
+                        object:nil];
+    // Register for background notification.
+    [defaultCenter addObserver:self
+                      selector:@selector(applicationDidEnterBackground:)
+                          name:UIApplicationDidEnterBackgroundNotification
+                        object:nil];
+    // Register for foregrounding notification.
+    [defaultCenter addObserver:self
+                      selector:@selector(applicationWillEnterForeground:)
+                          name:UIApplicationWillEnterForegroundNotification
+                        object:nil];
+
+    // Store pointer to |self| in |_browserState|.
+    _browserState->SetUserData(kTabModelKeyName, new TabModelHandle(self));
+  }
+  return self;
+}
+
+- (instancetype)init {
+  NOTREACHED();
+  return nil;
+}
+
+- (BOOL)restoreSessionWindow:(SessionWindowIOS*)window {
+  DCHECK(_browserState);
+  DCHECK(window);
+  if (!window.unclaimedSessions)
+    return NO;
+  size_t oldCount = [_tabs count];
+  size_t index = oldCount;
+  while (window.unclaimedSessions) {
+    std::unique_ptr<web::WebStateImpl> webState = [window nextSession];
+    DCHECK_EQ(webState->GetBrowserState(), _browserState);
+    Tab* tab = [self insertTabWithWebState:std::move(webState) atIndex:index++];
+    tab.webController.usePlaceholderOverlay = YES;
+    // Restore the CertificatePolicyCache. Note that after calling Pass()
+    // |webState| is invalid, so we need to get the webstate from |tab|.
+    UpdateCertificatePolicyCacheFromWebState(tab.webStateImpl);
+  }
+  DCHECK([_tabs count] > oldCount);
+  // If any tab was restored, the saved selected tab must be selected.
+  if ([_tabs count] > oldCount) {
+    NSUInteger selectedIndex = window.selectedIndex;
+    if (selectedIndex == NSNotFound)
+      selectedIndex = oldCount;
+    else
+      selectedIndex += oldCount;
+    DCHECK(selectedIndex < [_tabs count]);
+    Tab* newTab = [self tabAtIndex:selectedIndex];
+    DCHECK(newTab);
+    [self changeSelectedTabFrom:_currentTab to:newTab persistState:YES];
+
+    // If there was only one tab and it was the new tab page, clobber it.
+    if (oldCount == 1) {
+      Tab* tab = [_tabs objectAtIndex:0];
+      if (tab.url == GURL(kChromeUINewTabURL)) {
+        [self closeTab:tab];
+        if (_tabUsageRecorder)
+          _tabUsageRecorder->InitialRestoredTabs(_currentTab, _tabs);
+        return YES;
+      }
+    }
+    if (_tabUsageRecorder) {
+      _tabUsageRecorder->InitialRestoredTabs(
+          _currentTab,
+          [_tabs subarrayWithRange:NSMakeRange(oldCount,
+                                               [_tabs count] - oldCount)]);
+    }
+  }
+  return NO;
+}
+
+- (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)
+    return;
+  [_sessionService saveWindow:self.windowForSavingSession
+              forBrowserState:_browserState
+                  immediately:immediately];
+}
+
+- (Tab*)tabAtIndex:(NSUInteger)index {
+  return [_tabs objectAtIndex:index];
+}
+
+- (NSUInteger)indexOfTab:(Tab*)tab {
+  return [_tabs indexOfObject:tab];
+}
+
+- (Tab*)tabWithWindowName:(NSString*)windowName {
+  if (!windowName)
+    return nil;
+  for (Tab* tab in _tabs.get()) {
+    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 currentSessionID];
+  for (NSUInteger i = startIndex + 1; i < [_tabs count]; ++i) {
+    Tab* current = [_tabs objectAtIndex: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 currentSessionID];
+  // 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];
+    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 currentSessionID];
+  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];
+    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* opener = [tab navigationManager]->GetSessionController().openerId;
+  if (!opener.length)  // Short-circuit if opener is empty.
+    return nil;
+  for (Tab* iteratedTab in _tabs.get()) {
+    if ([[iteratedTab currentSessionID] isEqualToString:opener])
+      return iteratedTab;
+  }
+  return nil;
+}
+
+- (Tab*)insertOrUpdateTabWithURL:(const GURL&)URL
+                        referrer:(const web::Referrer&)referrer
+                      transition:(ui::PageTransition)transition
+                      windowName:(NSString*)windowName
+                          opener:(Tab*)parentTab
+                     openedByDOM:(BOOL)openedByDOM
+                         atIndex:(NSUInteger)index
+                    inBackground:(BOOL)inBackground {
+  web::NavigationManager::WebLoadParams params(URL);
+  params.referrer = referrer;
+  params.transition_type = transition;
+  return [self insertOrUpdateTabWithLoadParams:params
+                                    windowName:windowName
+                                        opener:parentTab
+                                   openedByDOM:openedByDOM
+                                       atIndex:index
+                                  inBackground:inBackground];
+}
+
+- (Tab*)insertOrUpdateTabWithLoadParams:
+            (const web::NavigationManager::WebLoadParams&)loadParams
+                             windowName:(NSString*)windowName
+                                 opener:(Tab*)parentTab
+                            openedByDOM:(BOOL)openedByDOM
+                                atIndex:(NSUInteger)index
+                           inBackground:(BOOL)inBackground {
+  // Find the tab for the given window name. If found, load with
+  // |originalParams| in it, otherwise create a new tab for it.
+  Tab* tab = [self tabWithWindowName:windowName];
+  if (tab) {
+    // Updating a tab shouldn't be possible with web usage suspended, since
+    // whatever page would be driving it should also be suspended.
+    DCHECK(webUsageEnabled_);
+
+    web::NavigationManager::WebLoadParams updatedParams(loadParams);
+    updatedParams.is_renderer_initiated = (parentTab != nil);
+    [tab.webController loadWithParams:updatedParams];
+
+    // Force the page to start loading even if it's in the background.
+    [tab.webController triggerPendingLoad];
+
+    if (!inBackground)
+      [self setCurrentTab:tab];
+  } else {
+    tab = [self insertTabWithLoadParams:loadParams
+                             windowName:windowName
+                                 opener:parentTab
+                            openedByDOM:openedByDOM
+                                atIndex:index
+                           inBackground:inBackground];
+  }
+
+  return tab;
+}
+
+- (Tab*)insertBlankTabWithTransition:(ui::PageTransition)transition
+                              opener:(Tab*)parentTab
+                         openedByDOM:(BOOL)openedByDOM
+                             atIndex:(NSUInteger)index
+                        inBackground:(BOOL)inBackground {
+  GURL emptyURL;
+  web::NavigationManager::WebLoadParams params(emptyURL);
+  params.transition_type = transition;
+  // Tabs open by DOM are always renderer initiated.
+  params.is_renderer_initiated = openedByDOM;
+  return [self insertTabWithLoadParams:params
+                            windowName:nil
+                                opener:parentTab
+                           openedByDOM:openedByDOM
+                               atIndex:index
+                          inBackground:inBackground];
+}
+
+- (Tab*)insertTabWithWebState:(std::unique_ptr<web::WebState>)webState
+                      atIndex:(NSUInteger)index {
+  DCHECK(_browserState);
+  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]);
+  [tab fetchFavicon];
+  [_tabs insertObject:tab atIndex:index];
+
+  [_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 {
+  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];
+
+  [_observers tabModel:self didMoveTab:tab fromIndex:fromIndex toIndex:toIndex];
+}
+
+- (void)replaceTab:(Tab*)oldTab
+           withTab:(Tab*)newTab
+    keepOldTabOpen:(BOOL)keepOldTabOpen {
+  NSUInteger index = [self indexOfTab:oldTab];
+  DCHECK_NE(NSNotFound, static_cast<NSInteger>(index));
+
+  base::scoped_nsobject<Tab> tabSaver([oldTab retain]);
+  [newTab fetchFavicon];
+  [_tabs replaceObjectAtIndex:index withObject:newTab];
+  [newTab setParentTabModel:self];
+
+  [_observers tabModel:self didReplaceTab:oldTab withTab:newTab atIndex:index];
+
+  if (self.currentTab == oldTab)
+    [self changeSelectedTabFrom:nil to:newTab persistState:NO];
+
+  [oldTab setParentTabModel:nil];
+  if (!keepOldTabOpen)
+    [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]];
+}
+
+- (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()) {
+    [tab terminateNetworkActivity];
+  }
+}
+
+- (void)notifyTabChanged:(Tab*)tab {
+  [_observers tabModel:self didChangeTab:tab];
+}
+
+- (void)addObserver:(id<TabModelObserver>)observer {
+  [_observers addObserver:observer];
+}
+
+- (void)removeObserver:(id<TabModelObserver>)observer {
+  [_observers removeObserver:observer];
+}
+
+- (void)resetSessionMetrics {
+  _closedTabCount = 0;
+  _openedTabCount = 0;
+  _newTabCount = 0;
+}
+
+- (void)recordSessionMetrics {
+  UMA_HISTOGRAM_CUSTOM_COUNTS("Session.ClosedTabCounts", _closedTabCount, 1,
+                              200, 50);
+  UMA_HISTOGRAM_CUSTOM_COUNTS("Session.OpenedTabCounts", _openedTabCount, 1,
+                              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()) {
+    [tab.webController reinitializeWebViewAndReload:(tab == _currentTab)];
+  }
+}
+
+- (void)setWebUsageEnabled:(BOOL)webUsageEnabled {
+  if (webUsageEnabled_ == webUsageEnabled)
+    return;
+  webUsageEnabled_ = webUsageEnabled;
+  for (Tab* tab in _tabs.get()) {
+    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()) {
+    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()) {
+    sessions::TabRestoreService::Tab* tab =
+        static_cast<sessions::TabRestoreService::Tab*>(entry.get());
+    int navigationIndex = tab->current_navigation_index;
+    sessions::SerializedNavigationEntry navigation =
+        tab->navigations[navigationIndex];
+    GURL URL = navigation.virtual_url();
+    if (UrlIsExternalFileReference(URL)) {
+      NSString* fileName = base::SysUTF8ToNSString(URL.ExtractFileName());
+      [referencedFiles addObject:fileName];
+    }
+  }
+  return referencedFiles;
+}
+
+// NOTE: This can be called multiple times, so must be robust against that.
+- (void)browserStateDestroyed {
+  [[NSNotificationCenter defaultCenter] removeObserver:self];
+  if (_browserState) {
+    _browserState->RemoveUserData(kTabModelKeyName);
+  }
+  _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];
+  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.webStateImpl),
+        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);
+
+  [_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];
+  } else {
+    [self saveSessionImmediately:NO];
+  }
+  base::RecordAction(base::UserMetricsAction("MobileTabClosed"));
+  ++_closedTabCount;
+}
+
+- (void)navigationCommittedInTab:(Tab*)tab {
+  if (self.offTheRecord)
+    return;
+  if (![tab navigationManager])
+    return;
+
+  // See if the navigation was within a page; if so ignore it.
+  web::NavigationItem* previousItem =
+      [tab navigationManager]->GetPreviousItem();
+  if (previousItem) {
+    GURL previousURL = previousItem->GetURL();
+    GURL currentURL = [tab navigationManager]->GetVisibleItem()->GetURL();
+
+    url::Replacements<char> replacements;
+    replacements.ClearRef();
+    if (previousURL.ReplaceComponents(replacements) ==
+        currentURL.ReplaceComponents(replacements)) {
+      return;
+    }
+  }
+
+  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];
+}
+
+#pragma mark - TabUsageRecorderDelegate
+
+- (NSUInteger)liveTabsCount {
+  NSUInteger count = 0;
+  NSArray* tabs = _tabs.get();
+  for (Tab* tab in tabs) {
+    if ([tab.webController isViewAlive])
+      count++;
+  }
+  return count;
+}
+
+#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
+  // window may never be saved (if another call comes in before the delay).
+  SessionWindowIOS* window = [[[SessionWindowIOS alloc] init] autorelease];
+  for (Tab* tab in _tabs.get()) {
+    DCHECK(tab.webStateImpl);
+    std::unique_ptr<web::WebStateImpl> webStateCopy(
+        tab.webStateImpl->CopyForSessionWindow());
+    [window addSession:std::move(webStateCopy)];
+  }
+  window.selectedIndex = [self indexOfTab:_currentTab];
+  return window;
+}
+
+- (BOOL)isNTPTab:(Tab*)tab {
+  std::string host = tab.url.host();
+  return host == kChromeUINewTabHost || host == kChromeUIBookmarksHost;
+}
+
+- (Tab*)insertTabWithLoadParams:
+            (const web::NavigationManager::WebLoadParams&)params
+                     windowName:(NSString*)windowName
+                         opener:(Tab*)parentTab
+                    openedByDOM:(BOOL)openedByDOM
+                        atIndex:(NSUInteger)index
+                   inBackground:(BOOL)inBackground {
+  DCHECK(_browserState);
+  base::scoped_nsobject<Tab> tab([[Tab alloc]
+      initWithWindowName:windowName
+                  opener:parentTab
+             openedByDOM:openedByDOM
+                   model:self
+            browserState:_browserState]);
+  [tab webController].webUsageEnabled = webUsageEnabled_;
+
+  if ((PageTransitionCoreTypeIs(params.transition_type,
+                                ui::PAGE_TRANSITION_LINK)) &&
+      (index == TabModelConstants::kTabPositionAutomatically)) {
+    DCHECK(!parentTab || [self indexOfTab:parentTab] != NSNotFound);
+    // Assume tabs opened via link clicks are part of the same "task" as their
+    // parent and are grouped together.
+    TabModelOrderConstants::InsertionAdjacency adjacency =
+        inBackground ? TabModelOrderConstants::kAdjacentAfter
+                     : TabModelOrderConstants::kAdjacentBefore;
+    index = [_orderController insertionIndexForTab:tab
+                                        transition:params.transition_type
+                                            opener:parentTab
+                                         adjacency:adjacency];
+  } else {
+    // For all other types, respect what was passed to us, normalizing values
+    // that are too large.
+    if (index >= self.count)
+      index = [_orderController insertionIndexForAppending];
+  }
+
+  if (PageTransitionCoreTypeIs(params.transition_type,
+                               ui::PAGE_TRANSITION_TYPED) &&
+      index == self.count) {
+    // Also, any tab opened at the end of the TabStrip with a "TYPED"
+    // transition inherit group as well. This covers the cases where the user
+    // creates a New Tab (e.g. Ctrl+T, or clicks the New Tab button), or types
+    // in the address bar and presses Alt+Enter. This allows for opening a new
+    // Tab to quickly look up something. When this Tab is closed, the old one
+    // is re-selected, not the next-adjacent.
+    // TODO(crbug.com/661988): Make this work.
+  }
+
+  [self insertTab:tab atIndex:index];
+
+  if (!inBackground && _tabUsageRecorder)
+    _tabUsageRecorder->TabCreatedForSelection(tab);
+
+  [[tab webController] loadWithParams:params];
+  // Force the page to start loading even if it's in the background.
+  if (webUsageEnabled_)
+    [[tab webController] triggerPendingLoad];
+  NSDictionary* userInfo = @{
+    kTabModelTabKey : tab,
+    kTabModelOpenInBackgroundKey : @(inBackground),
+  };
+  [[NSNotificationCenter defaultCenter]
+      postNotificationName:kTabModelNewTabWillOpenNotification
+                    object:self
+                  userInfo:userInfo];
+
+  if (!inBackground)
+    [self setCurrentTab:tab];
+
+  return tab;
+}
+
+- (void)changeSelectedTabFrom:(Tab*)oldTab
+                           to:(Tab*)newTab
+                 persistState:(BOOL)persist {
+  if (oldTab) {
+    // Save state, such as scroll position, before switching tabs.
+    if (oldTab != newTab && persist)
+      [oldTab recordStateInHistory];
+    [self postNotificationName:kTabModelTabDeselectedNotification
+                       withTab:oldTab];
+  }
+
+  // No Tab to select (e.g. the last Tab has been closed).
+  if ([self indexOfTab:newTab] == NSNotFound)
+    return;
+
+  _currentTab.reset(newTab);
+  if (newTab) {
+    [_observers tabModel:self
+        didChangeActiveTab:newTab
+               previousTab:oldTab
+                   atIndex:[self indexOfTab:newTab]];
+    [newTab updateLastVisitedTimestamp];
+    ++_openedTabCount;
+  }
+  BOOL loadingFinished = [newTab.webController loadPhase] == web::PAGE_LOADED;
+  if (loadingFinished) {
+    // Persist the session state.
+    [self saveSessionImmediately:NO];
+  }
+}
+
+- (void)updateSnapshotCache:(Tab*)tab {
+  NSMutableSet* set = [NSMutableSet set];
+  NSUInteger index = [self indexOfTab:tab];
+  if (index > 0) {
+    Tab* previousTab = [self tabAtIndex:(index - 1)];
+    [set addObject:[previousTab currentSessionID]];
+  }
+  if (index < self.count - 1) {
+    Tab* nextTab = [self tabAtIndex:(index + 1)];
+    [set addObject:[nextTab currentSessionID]];
+  }
+  [SnapshotCache sharedInstance].pinnedIDs = set;
+}
+
+- (void)postNotificationName:(NSString*)notificationName withTab:(Tab*)tab {
+  // A scoped_nsobject is used rather than an NSDictionary with static
+  // initializer dictionaryWithObject, because that approach adds the dictionary
+  // to the autorelease pool, which in turn holds Tab alive longer than
+  // necessary.
+  base::scoped_nsobject<NSDictionary> userInfo(
+      [[NSDictionary alloc] initWithObjectsAndKeys:tab, kTabModelTabKey, nil]);
+  [[NSNotificationCenter defaultCenter] postNotificationName:notificationName
+                                                      object:self
+                                                    userInfo:userInfo];
+}
+
+#pragma mark - Notification Handlers
+
+// Called when UIApplicationWillResignActiveNotification is received.
+- (void)willResignActive:(NSNotification*)notify {
+  if (webUsageEnabled_ && _currentTab) {
+    [[SnapshotCache sharedInstance]
+        willBeSavedGreyWhenBackgrounding:[_currentTab currentSessionID]];
+  }
+}
+
+// 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.
+  scoped_refptr<web::CertificatePolicyCache> policy_cache =
+      web::BrowserState::GetCertificatePolicyCache(_browserState);
+  DCHECK(policy_cache);
+  web::WebThread::PostTask(
+      web::WebThread::IO, FROM_HERE,
+      base::Bind(&CleanCertificatePolicyCache, policy_cache, _tabs));
+
+  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) {
+    [[SnapshotCache sharedInstance]
+        saveGreyInBackgroundForSessionID:[_currentTab currentSessionID]];
+  }
+}
+
+// Called when UIApplicationWillEnterForegroundNotification is received.
+- (void)applicationWillEnterForeground:(NSNotification*)notify {
+  if (_tabUsageRecorder) {
+    _tabUsageRecorder->AppWillEnterForeground();
+  }
+}
+
+@end
+
+@implementation TabModel (PrivateForTestingOnly)
+
+- (Tab*)addTabWithURL:(const GURL&)URL
+             referrer:(const web::Referrer&)referrer
+           windowName:(NSString*)windowName {
+  return [self insertTabWithURL:URL
+                       referrer:referrer
+                     windowName:windowName
+                         opener:nil
+                        atIndex:[_orderController insertionIndexForAppending]];
+}
+
+- (Tab*)insertTabWithURL:(const GURL&)URL
+                referrer:(const web::Referrer&)referrer
+              windowName:(NSString*)windowName
+                  opener:(Tab*)parentTab
+                 atIndex:(NSUInteger)index {
+  DCHECK(_browserState);
+  base::scoped_nsobject<Tab> tab([[Tab alloc]
+      initWithWindowName:windowName
+                  opener:parentTab
+             openedByDOM:NO
+                   model:self
+            browserState:_browserState]);
+  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