[ios] WebStateList owns all WebState it manages.

ios/chrome/browser/tabs/tab_model_web_state_list_delegate.mm

Index: ios/chrome/browser/tabs/tab_model_web_state_list_delegate.mm
diff --git a/ios/chrome/browser/tabs/tab_model_web_state_list_delegate.mm b/ios/chrome/browser/tabs/tab_model_web_state_list_delegate.mm
index 0c5a4fb5cc0305d262de3fe4d29331e24f881e15..253cf3f3c4f826e0b4a27a48dd9260986e7379e7 100644
--- a/ios/chrome/browser/tabs/tab_model_web_state_list_delegate.mm
+++ b/ios/chrome/browser/tabs/tab_model_web_state_list_delegate.mm
@@ -5,6 +5,9 @@
 #import "ios/chrome/browser/tabs/tab_model_web_state_list_delegate.h"
 
 #include "base/logging.h"
+#import "ios/chrome/browser/tabs/legacy_tab_helper.h"
+#import "ios/chrome/browser/tabs/tab.h"
+#import "ios/chrome/browser/tabs/tab_helper_util.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
@@ -17,6 +20,19 @@ TabModelWebStateListDelegate::TabModelWebStateListDelegate(TabModel* tab_model)
 
 TabModelWebStateListDelegate::~TabModelWebStateListDelegate() = default;
 
-void TabModelWebStateListDelegate::WillAddWebState(web::WebState* web_state) {}
+void TabModelWebStateListDelegate::WillAddWebState(web::WebState* web_state) {
+  // Some Tab objects are created outside of TabModel, avoid recreating the
+  // tab helpers for those Tab objects.
+  if (!LegacyTabHelper::FromWebState(web_state))
+    AttachTabHelpers(web_state);
 
-void TabModelWebStateListDelegate::WebStateDetached(web::WebState* web_state) {}
+  DCHECK(LegacyTabHelper::FromWebState(web_state));
+  Tab* tab = LegacyTabHelper::GetTabForWebState(web_state);
+  [tab setParentTabModel:tab_model_.get()];
+}
+
+void TabModelWebStateListDelegate::WebStateDetached(web::WebState* web_state) {
+  DCHECK(LegacyTabHelper::FromWebState(web_state));
+  Tab* tab = LegacyTabHelper::GetTabForWebState(web_state);
+  [tab setParentTabModel:nil];
+}