Reserve a virtual method for use with a feature in Qt 5.1.

The view will query the delegate for roles which are relevant to
the particular delegate. For unrelated roles, the delegate
will not have to repaint when the data changes.

Change-Id: If8f1ba4c2bce7dbcf70de344b984aea1deca0edd
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: David Faure <faure@kde.org>

src/widgets/itemviews/qabstractitemdelegate.cpp

@@ -402,6 +402,16 @@ bool QAbstractItemDelegate::helpEvent(QHelpEvent *event,
     return false;
 }
 
+/*!
+    \internal
+
+    This virtual method is reserved and will be used in Qt 5.1.
+*/
+QSet<int> QAbstractItemDelegate::paintingRoles() const
+{
+    return QSet<int>();
+}
+
 QT_END_NAMESPACE
 
 #endif // QT_NO_ITEMVIEWS

src/widgets/itemviews/qabstractitemdelegate.h

@@ -114,6 +114,8 @@ public:
                            const QStyleOptionViewItem &option,
                            const QModelIndex &index);
 
+    virtual QSet<int> paintingRoles() const;
+
 Q_SIGNALS:
     void commitData(QWidget *editor);
     void closeEditor(QWidget *editor, QAbstractItemDelegate::EndEditHint hint = NoHint);