Replace TabModel with WebStateList in GoogleLandingController.

ios/chrome/browser/ui/ntp/google_landing_mediator.mm

Index: ios/chrome/browser/ui/ntp/google_landing_mediator.mm
diff --git a/ios/chrome/browser/ui/ntp/google_landing_mediator.mm b/ios/chrome/browser/ui/ntp/google_landing_mediator.mm
index 1014342bbe35d77393c40f821de8ef7d37025e3a..a5a03eabc0491bd4392d20f00a386e3376b58223 100644
--- a/ios/chrome/browser/ui/ntp/google_landing_mediator.mm
+++ b/ios/chrome/browser/ui/ntp/google_landing_mediator.mm
@@ -31,6 +31,8 @@
 #import "ios/chrome/browser/ui/ntp/notification_promo_whats_new.h"
 #import "ios/chrome/browser/ui/toolbar/web_toolbar_controller.h"
 #import "ios/chrome/browser/ui/url_loader.h"
+#import "ios/chrome/browser/web_state_list/web_state_list.h"
+#import "ios/chrome/browser/web_state_list/web_state_list_observer_bridge.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #include "ios/public/provider/chrome/browser/voice/voice_search_provider.h"
 
@@ -79,7 +81,8 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
 
 }  // namespace google_landing
 
-@interface GoogleLandingMediator ()<MostVisitedSitesObserving> {
+@interface GoogleLandingMediator ()<MostVisitedSitesObserving,
+                                    WebStateListObserving> {
   // The ChromeBrowserState associated with this mediator.
   ios::ChromeBrowserState* _browserState;  // Weak.
 
@@ -112,7 +115,9 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
 
   base::WeakNSProtocol<id<WebToolbarDelegate>> _webToolbarDelegate;
 
-  base::scoped_nsobject<TabModel> _tabModel;
+  // Observes the WebStateList so that this mediator can update the UI when the
+  // active WebState changes.
+  std::unique_ptr<WebStateListObserverBridge> _webStateListObserver;
 
   // What's new promo.
   std::unique_ptr<NotificationPromoWhatsNew> _notification_promo;
@@ -121,6 +126,9 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
 // Consumer to handle google landing update notifications.
 @property(nonatomic) id<GoogleLandingConsumer> consumer;
 
+// The WebStateList that is being observed by this mediator.
+@property(nonatomic, assign) WebStateList* webStateList;
+
 // Perform initial setup.
 - (void)setUp;
 
@@ -129,13 +137,14 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
 @implementation GoogleLandingMediator
 
 @synthesize consumer = _consumer;
+@synthesize webStateList = _webStateList;
 
 - (instancetype)initWithConsumer:(id<GoogleLandingConsumer>)consumer
                     browserState:(ios::ChromeBrowserState*)browserState
                           loader:(id<UrlLoader>)loader
                          focuser:(id<OmniboxFocuser>)focuser
               webToolbarDelegate:(id<WebToolbarDelegate>)webToolbarDelegate
-                        tabModel:(TabModel*)tabModel {
+                    webStateList:(WebStateList*)webStateList {
   self = [super init];
   if (self) {
     _consumer = consumer;
@@ -143,13 +152,18 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
     _loader = loader;
     _focuser.reset(focuser);
     _webToolbarDelegate.reset(webToolbarDelegate);
-    _tabModel.reset([tabModel retain]);
+    _webStateList = webStateList;
+
+    _webStateListObserver = base::MakeUnique<WebStateListObserverBridge>(self);
+    _webStateList->AddObserver(_webStateListObserver.get());
+
     [self setUp];
   }
   return self;
 }
 
 - (void)dealloc {
+  _webStateList->RemoveObserver(_webStateListObserver.get());
   [[NSNotificationCenter defaultCenter] removeObserver:self.consumer];
   [super dealloc];
 }
@@ -161,6 +175,7 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
                                          ->IsVoiceSearchEnabled()];
   [_consumer
       setMaximumMostVisitedSitesShown:[GoogleLandingMediator maxSitesShown]];
+  [_consumer setTabCount:self.webStateList->count()];
 
   // Set up template URL service to listen for default search engine changes.
   _templateURLService =
@@ -249,6 +264,20 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
   }
 }
 
+#pragma mark - WebStateListObserving
+
+- (void)webStateList:(WebStateList*)webStateList
+    didInsertWebState:(web::WebState*)webState
+              atIndex:(int)index {
+  [self.consumer setTabCount:self.webStateList->count()];
+}
+
+- (void)webStateList:(WebStateList*)webStateList
+    didDetachWebState:(web::WebState*)webState
+              atIndex:(int)atIndex {
+  [self.consumer setTabCount:self.webStateList->count()];
+}
+
 #pragma mark - GoogleLandingDataSource
 
 - (void)addBlacklistedURL:(const GURL&)url {
@@ -292,10 +321,6 @@ void SearchEngineObserver::OnTemplateURLServiceChanged() {
   return _webToolbarDelegate;
 }
 
-- (TabModel*)tabModel {
-  return _tabModel;
-}
-
 - (void)promoViewed {
   DCHECK(_notification_promo);
   _notification_promo->HandleViewed();