Fix ios_chrome_unittests to crash on DCHECK failure.

ios/chrome/browser/ui/settings/personal_data_manager_data_changed_observer.h

+// 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.
+
+#ifndef IOS_CHROME_BROWSER_UI_SETTINGS_PERSONAL_DATA_MANAGER_DATA_CHANGED_OBSERVER_H_
+#define IOS_CHROME_BROWSER_UI_SETTINGS_PERSONAL_DATA_MANAGER_DATA_CHANGED_OBSERVER_H_
+
+#include "base/macros.h"
+#include "base/run_loop.h"
+#include "components/autofill/core/browser/personal_data_manager_observer.h"
+
+namespace autofill {
+class PersonalDataManager;
+}
+
+// Helper class to allow waiting until the asynchronous operation on the
+// autofill::PersonalDataManager completed. Need to be used like this:
+//
+//   autofill::PersonalDataManager* personal_data_manager = ...;
+//   PersonalDataManagerDataChangedObserver observer(personal_data_manager);
+//   personal_data_manager->...();  // Starts some asynchronous operation.
+//   observer.Wait();
+//
+class PersonalDataManagerDataChangedObserver
+    : public autofill::PersonalDataManagerObserver {
+ public:
+  PersonalDataManagerDataChangedObserver(
+      autofill::PersonalDataManager* personal_data_manager);
+  ~PersonalDataManagerDataChangedObserver() override;
+
+  // Blocks until |OnPersonalDataChanged| is invoked at the end of the
+  // asynchronous modification on the PersonalDataManager.
+  void Wait();
+
+  // autofill::PersonalDataManagerObserver implementation.
+  void OnPersonalDataChanged() override;
+
+ private:
+  autofill::PersonalDataManager* personal_data_manager_;
+  base::RunLoop run_loop_;
+
+  DISALLOW_COPY_AND_ASSIGN(PersonalDataManagerDataChangedObserver);
+};
+
+#endif  // IOS_CHROME_BROWSER_UI_SETTINGS_PERSONAL_DATA_MANAGER_DATA_CHANGED_OBSERVER_H_