WebStateList is an array of web::WebState* wrappers.

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 = [
     "tab.h",
     "tab_delegate.h",
     "tab_dialog_delegate.h",
     "tab_headers_delegate.h",
     "tab_model.h",
     "tab_model_list.h",
     "tab_model_observer.h",
     "tab_model_order_controller.h",
     "tab_model_synced_window_delegate.h",
     "tab_model_synced_window_delegate_getter.h",
     "tab_private.h",
     "tab_snapshotting_delegate.h",
+    "web_state_handle.h",
+    "web_state_list.h",
   ]
   deps = [
     "//components/sessions",
     "//components/signin/ios/browser",
     "//components/sync_sessions",
     "//ios/net",
     "//ios/web",
     "//ui/base",
   ]
   libs = [ "UIKit.framework" ]
@@ skipping 81 matching lines @@
   allow_circular_includes_from = [ ":tabs_internal_arc" ]
   libs = [
     "CoreLocation.framework",
     "UIKit.framework",
   ]
 }
 
 source_set("tabs_internal_arc") {
   sources = [
     "tab_model_list.mm",
+    "web_state_list.mm",
   ]
   deps = [
     ":tabs",
     "//base",
     "//ios/chrome/browser",
     "//ios/chrome/browser/browser_state",
   ]
   libs = [ "Foundation.framework" ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }
@@ skipping 44 matching lines @@
     ":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" ]
 }