Fold AppModalDialog into its only subclass, JavaScriptAppModalDialog.

chrome/browser/extensions/alert_apitest.cc

Index: chrome/browser/extensions/alert_apitest.cc
diff --git a/chrome/browser/extensions/alert_apitest.cc b/chrome/browser/extensions/alert_apitest.cc
index 9d638b961d80b963c90ddc581c3fde2ade0847ba..f32e415906874cd3c29ee31f9c411d39f9b58b32 100644
--- a/chrome/browser/extensions/alert_apitest.cc
+++ b/chrome/browser/extensions/alert_apitest.cc
@@ -10,7 +10,6 @@
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/test/base/ui_test_utils.h"
-#include "components/app_modal/app_modal_dialog.h"
 #include "components/app_modal/app_modal_dialog_queue.h"
 #include "components/app_modal/javascript_app_modal_dialog.h"
 #include "components/app_modal/native_app_modal_dialog.h"
@@ -25,11 +24,9 @@ namespace {
 void GetNextDialog(app_modal::NativeAppModalDialog** native_dialog) {
   DCHECK(native_dialog);
   *native_dialog = nullptr;
-  app_modal::AppModalDialog* dialog = ui_test_utils::WaitForAppModalDialog();
-  ASSERT_TRUE(dialog->IsJavaScriptModalDialog());
-  app_modal::JavaScriptAppModalDialog* js_dialog =
-      static_cast<app_modal::JavaScriptAppModalDialog*>(dialog);
-  *native_dialog = js_dialog->native_dialog();
+  app_modal::JavaScriptAppModalDialog* dialog =
+      ui_test_utils::WaitForAppModalDialog();
+  *native_dialog = dialog->native_dialog();
   ASSERT_TRUE(*native_dialog);
 }