transientParent property for Dialog

use it when a Dialog instance is a popup menu of another dialog

src/declarativeimports/core/dialog.cpp

@@ -679,6 +679,16 @@ void DialogProxy::updateInputShape()
 #endif
 }
 
+void DialogProxy::setTransientParentAndNotify(QWindow *parent)
+{
+    if (parent == transientParent()) {
+        return;
+    }
+
+    setTransientParent(parent);
+    emit transientParentChanged();
+}
+
 
 //find the screen which contains the item
 QScreen* DialogProxy::screenForItem(QQuickItem* item) const

src/declarativeimports/core/dialog.h

@@ -76,6 +76,11 @@ class DialogProxy : public QQuickWindow, public QQmlParserStatus
      */
     Q_PROPERTY(WindowType type READ type WRITE setType NOTIFY typeChanged)
 
+    /**
+     * This is a hint to the window manager that this window is a dialog or pop-up on behalf of the given window.
+     */
+    Q_PROPERTY(QWindow *transientParent READ transientParent WRITE setTransientParentAndNotify NOTIFY transientParentChanged)
+
     /**
      * Whether the dialog should be hidden when the dialog loses focus.
      *
@@ -141,6 +146,8 @@ public:
     bool isOutputOnly() const;
     void updateInputShape();
 
+    void setTransientParentAndNotify(QWindow *parent);
+
 Q_SIGNALS:
     void mainItemChanged();
     void locationChanged();
@@ -148,6 +155,7 @@ Q_SIGNALS:
     void typeChanged();
     void hideOnWindowDeactivateChanged();
     void outputOnlyChanged();
+    void transientParentChanged();
 
 public Q_SLOTS:
     void syncMainItemToSize();