[ios] Extend WebStateListObserver amd WebStateListDelegate APIs.

ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.h

Index: ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.h
diff --git a/ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.h b/ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.h
index e412fb288dd13cd99c2d34959ebe4636d16ffc58..aeb9a54083bc6954299ed9b2e88705dace36479c 100644
--- a/ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.h
+++ b/ios/shared/chrome/browser/tabs/web_state_list_observer_bridge.h
@@ -33,13 +33,25 @@
 - (void)webStateList:(WebStateList*)webStateList
     didReplaceWebState:(web::WebState*)oldWebState
           withWebState:(web::WebState*)newWebState
-               atIndex:(int)index;
+               atIndex:(int)atIndex;
+
+// Invoked before the specified WebState is detached from the WebStateList.
+// The WebState is still valid and still in the WebStateList.
+- (void)webStateList:(WebStateList*)webStateList
+    willDetachWebState:(web::WebState*)webState
+               atIndex:(int)atIndex;
 
 // Invoked after the WebState at the specified index has been detached. The
 // WebState is still valid but is no longer in the WebStateList.
 - (void)webStateList:(WebStateList*)webStateList
     didDetachWebState:(web::WebState*)webState
-              atIndex:(int)index;
+              atIndex:(int)atIndex;
+
+// Invoked before the specified WebState is destroyed via the WebStateList.
+// The WebState is still valid but is no longer in the WebStateList.
+- (void)webStateList:(WebStateList*)webStateList
+    willCloseWebState:(web::WebState*)webState
+              atIndex:(int)atIndex;
 
 // Invoked after |newWebState| was activated at the specified index. Both
 // WebState are either valid or null (if there was no selection or there is
@@ -73,9 +85,15 @@ class WebStateListObserverBridge : public WebStateListObserver {
                           web::WebState* old_web_state,
                           web::WebState* new_web_state,
                           int index) override;
+  void WillDetachWebStateAt(WebStateList* web_state_list,
+                            web::WebState* web_state,
+                            int index) override;
   void WebStateDetachedAt(WebStateList* web_state_list,
                           web::WebState* web_state,
                           int index) override;
+  void WillCloseWebStateAt(WebStateList* web_state_list,
+                           web::WebState* web_state,
+                           int index) override;
   void WebStateActivatedAt(WebStateList* web_state_list,
                            web::WebState* old_web_state,
                            web::WebState* new_web_state,