ADS: Remove struct from DockAreaTabBar

We do not use struct in Qt Creator.

Change-Id: Id9abb6f3a5a4f4406fbefa24735e5f7e1215eeb4
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/advanceddockingsystem/dockareatabbar.cpp

@@ -59,8 +59,9 @@ namespace ADS
     /**
      * Private data class of DockAreaTabBar class (pimpl)
      */
-    struct DockAreaTabBarPrivate
+    class DockAreaTabBarPrivate
     {
+    public:
         DockAreaTabBar *q;
         DockAreaWidget *m_dockArea;
         QWidget *m_tabsContainerWidget;
@@ -87,8 +88,7 @@ namespace ADS
          * Convenience function to access last tab
          */
         DockWidgetTab *lastTab() const {return q->tab(q->count() - 1);}
-    };
-    // struct DockAreaTabBarPrivate
+    }; // class DockAreaTabBarPrivate
 
     DockAreaTabBarPrivate::DockAreaTabBarPrivate(DockAreaTabBar *parent)
         : q(parent)

src/libs/advanceddockingsystem/dockareatabbar.h

@@ -43,7 +43,7 @@ namespace ADS {
 
 class DockAreaWidget;
 class DockWidgetTab;
-struct DockAreaTabBarPrivate;
+class DockAreaTabBarPrivate;
 class DockAreaTitleBar;
 class FloatingDockContainer;
 class AbstractFloatingWidget;
@@ -62,7 +62,7 @@ class ADS_EXPORT DockAreaTabBar : public QScrollArea
     Q_OBJECT
 private:
     DockAreaTabBarPrivate *d; ///< private data (pimpl)
-    friend struct DockAreaTabBarPrivate;
+    friend class DockAreaTabBarPrivate;
     friend class DockAreaTitleBar;
 
     void onTabClicked();