Support non-desktop platforms better with QDragManager.

By default QDragManager brings in a number of "desktopisms" (e.g. that
a drag is always controlled by mouse events, can be cancelled with some
key press, etc.), these assumptions are not necessarily suitable for
all QPA platforms. Therefore there has to be a way to disable this
built-in event handling, and let the QPlaformDrag decide how the drag
is controlled and when it ends.

Change-Id: Ie9fa2df7ba1e30dd1c6e2cff406490e36be73c4f
Reviewed-on: http://codereview.qt.nokia.com/2085
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

src/gui/kernel/qdnd.cpp

@@ -511,6 +511,24 @@ void QDragManager::cancel(bool deleteSource)
     global_accepted_action = Qt::IgnoreAction;
 }
 
+/*!
+  Called from startDrag() in QPlatformDrag implementations that do not need
+  the desktop-oriented stuff provided by the event filter (e.g. because their
+  drag is not based on mouse events). Instead, they will manage everything on
+  their own, will not rely on move/drop/cancel, and will call stopDrag() to stop
+  the event loop when the drag is over.
+ */
+void QDragManager::unmanageEvents()
+{
+    qApp->removeEventFilter(this);
+}
+
+void QDragManager::stopDrag()
+{
+    if (eventLoop)
+        eventLoop->exit();
+}
+
 #endif // QT_NO_DRAGANDDROP
 
 #if !(defined(QT_NO_DRAGANDDROP) && defined(QT_NO_CLIPBOARD))

src/gui/kernel/qdnd_p.h

@@ -200,6 +200,9 @@ public:
 
     QShapedPixmapWindow *shapedPixmapWindow;
 
+    void unmanageEvents();
+    void stopDrag();
+
 private:
     QMimeData *platformDropData;