[ios] WebStateList owns all WebState it manages.

ios/chrome/browser/tabs/BUILD.gn

 # Copyright 2016 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.
 
 source_set("tabs") {
   sources = [
     "legacy_tab_helper.h",
     "tab.h",
     "tab_delegate.h",
     "tab_dialog_delegate.h",
     "tab_headers_delegate.h",
+    "tab_helper_util.h",
     "tab_model.h",
     "tab_model_list.h",
     "tab_model_observer.h",
     "tab_model_synced_window_delegate.h",
     "tab_model_synced_window_delegate_getter.h",
     "tab_private.h",
     "tab_snapshotting_delegate.h",
   ]
   deps = [
     "//components/sessions",
@@ skipping 88 matching lines @@
   allow_circular_includes_from = [ ":tabs_internal_arc" ]
   libs = [
     "CoreLocation.framework",
     "UIKit.framework",
   ]
 }
 
 source_set("tabs_internal_arc") {
   sources = [
     "legacy_tab_helper.mm",
-    "tab_helper_util.h",
     "tab_helper_util.mm",
+    "tab_model_closing_web_state_observer.h",
+    "tab_model_closing_web_state_observer.mm",
     "tab_model_list.mm",
     "tab_model_observers.h",
     "tab_model_observers.mm",
     "tab_model_observers_bridge.h",
     "tab_model_observers_bridge.mm",
     "tab_model_selected_tab_observer.h",
     "tab_model_selected_tab_observer.mm",
     "tab_model_web_state_list_delegate.h",
     "tab_model_web_state_list_delegate.mm",
     "tab_parenting_observer.h",
     "tab_parenting_observer.mm",
   ]
   deps = [
     ":tabs",
     "//base",
     "//components/favicon/ios",
     "//components/history/core/browser",
     "//components/history/ios/browser",
     "//components/keyed_service/core",
+    "//components/sessions",
     "//components/signin/ios/browser",
     "//ios/chrome/browser",
     "//ios/chrome/browser/bookmarks",
     "//ios/chrome/browser/browser_state",
     "//ios/chrome/browser/favicon",
     "//ios/chrome/browser/find_in_page",
     "//ios/chrome/browser/find_in_page",
     "//ios/chrome/browser/history",
     "//ios/chrome/browser/infobars",
     "//ios/chrome/browser/reading_list",
     "//ios/chrome/browser/sessions",
     "//ios/chrome/browser/signin",
     "//ios/chrome/browser/ssl",
     "//ios/chrome/browser/store_kit",
     "//ios/chrome/browser/sync",
     "//ios/chrome/browser/translate",
     "//ios/chrome/browser/web",
     "//ios/chrome/browser/web:web_internal",
     "//ios/public/provider/chrome/browser",
     "//ios/shared/chrome/browser/tabs",
     "//ios/web",
+    "//url",
   ]
   libs = [ "Foundation.framework" ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "tab_model_unittest.mm",
     "tab_unittest.mm",
@@ skipping 12 matching lines @@
     "//ios/chrome/browser/history",
     "//ios/chrome/browser/infobars",
     "//ios/chrome/browser/sessions",
     "//ios/chrome/browser/sessions:test_support",
     "//ios/chrome/browser/ui:ui_internal",
     "//ios/chrome/browser/web:web_internal",
     "//ios/chrome/test:test_support",
     "//ios/public/provider/chrome/browser",
     "//ios/public/provider/chrome/browser:test_support",
     "//ios/public/provider/chrome/browser/native_app_launcher:test_support",
+    "//ios/shared/chrome/browser/tabs",
     "//ios/testing:ocmock_support",
     "//ios/web",
     "//ios/web:test_support",
     "//net",
     "//testing/gtest",
     "//third_party/ocmock",
   ]
 }
 
 source_set("unit_tests_arc") {
   testonly = true
   sources = [
     "tab_model_list_unittest.mm",
   ]
   deps = [
     ":tabs",
     ":tabs_internal",
     "//base",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/chrome/browser/sessions:test_support",
     "//ios/web:test_support",
     "//testing/gtest",
   ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }