Linux native notifications: Add initial unit test

chrome/browser/notifications/notification_platform_bridge_linux.h

 // Copyright 2017 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 CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_PLATFORM_BRIDGE_LINUX_H_
 #define CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_PLATFORM_BRIDGE_LINUX_H_
 
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/notifications/notification_platform_bridge.h"
 
 class NotificationPlatformBridgeLinuxImpl;
 
+namespace dbus {
+class Bus;
+}
+
 class NotificationPlatformBridgeLinux : public NotificationPlatformBridge {
  public:
   NotificationPlatformBridgeLinux();
 
   ~NotificationPlatformBridgeLinux() override;
 
   // NotificationPlatformBridge:
   void Display(NotificationCommon::Type notification_type,
                const std::string& notification_id,
                const std::string& profile_id,
                bool is_incognito,
                const Notification& notification) override;
   void Close(const std::string& profile_id,
              const std::string& notification_id) override;
   void GetDisplayed(
       const std::string& profile_id,
       bool incognito,
       const GetDisplayedNotificationsCallback& callback) const override;
   void SetReadyCallback(NotificationBridgeReadyCallback callback) override;
 
  private:
+  friend class NotificationPlatformBridgeLinuxTest;
+
+  // Constructor only used in unit testing.
+  explicit NotificationPlatformBridgeLinux(scoped_refptr<dbus::Bus> bus);
+
+  void CleanUp();
+
   scoped_refptr<NotificationPlatformBridgeLinuxImpl> impl_;
 
   DISALLOW_COPY_AND_ASSIGN(NotificationPlatformBridgeLinux);
 };
 
 #endif  // CHROME_BROWSER_NOTIFICATIONS_NOTIFICATION_PLATFORM_BRIDGE_LINUX_H_