[ios] WebStateList owns all WebState it manages.

ios/chrome/browser/tabs/tab_private.h

Index: ios/chrome/browser/tabs/tab_private.h
diff --git a/ios/chrome/browser/tabs/tab_private.h b/ios/chrome/browser/tabs/tab_private.h
index 6be2b01a0ac7eaf46034f73b787564ebcabe67ba..6f179ec3ac607c31f3c22c0a56839904cae7715d 100644
--- a/ios/chrome/browser/tabs/tab_private.h
+++ b/ios/chrome/browser/tabs/tab_private.h
@@ -26,10 +26,20 @@ class WebStateImpl;
 // Replaces the existing |externalAppLauncher_|.
 - (void)replaceExternalAppLauncher:(id)externalAppLauncher;
 
-- (TabModel*)parentTabModel;
-
 - (FormInputAccessoryViewController*)inputAccessoryViewController;
 
 @end
 
+@interface Tab (Private)
+
+// Attaches tab helper-like objects for AttachTabHelpers. Those objects should
+// be converted in real tab helpers and created by AttachTabHelpers.
+- (void)attachTabHelpers;
+
+// Cleans up the Tab after the associated WebState object has been destroyed.
+// Called by LegacyTabHelper. Do *not* call this method directly.
+- (void)onWebStateDestroyed;
+
+@end
+
 #endif  // IOS_CHROME_BROWSER_TABS_TAB_PRIVATE_H_