QRegion: add move ctor

After this change, this was the distribution of calls in
QtGui and QtWidgets when the patch was developed for 5.4:

      QtGui  QtWidgets
move  23     63
copy  23     36

Change-Id: If3f536e52fc242c585e7fa0662049c0657efcc9c
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

src/gui/painting/qregion.cpp

@@ -209,6 +209,16 @@ QT_BEGIN_NAMESPACE
     Constructs a new region which is equal to region \a r.
 */
 
+/*!
+    \fn QRegion::QRegion(QRegion &&other)
+    \since 5.7
+
+    Move-constructs a new region from region \a other.
+    After the call, \a other is null.
+
+    \sa isNull()
+*/
+
 /*!
     \fn QRegion::QRegion(const QBitmap &bm)
 

src/gui/painting/qregion.h

@@ -68,6 +68,8 @@ public:
     QRegion(const QRect &r, RegionType t = Rectangle);
     QRegion(const QPolygon &pa, Qt::FillRule fillRule = Qt::OddEvenFill);
     QRegion(const QRegion &region);
+    QRegion(QRegion &&other) Q_DECL_NOTHROW
+        : d(other.d) { other.d = const_cast<QRegionData*>(&shared_empty); }
     QRegion(const QBitmap &bitmap);
     ~QRegion();
     QRegion &operator=(const QRegion &);

tests/auto/gui/painting/qregion/tst_qregion.cpp

@@ -45,6 +45,7 @@ public:
     tst_QRegion();
 
 private slots:
+    void moveSemantics();
     void boundingRect();
     void rects();
     void swap();
@@ -93,6 +94,28 @@ tst_QRegion::tst_QRegion()
 {
 }
 
+void tst_QRegion::moveSemantics()
+{
+    const QRegion rect(QRect(0, 0, 100, 100));
+
+    // move assignment
+    {
+        QRegion r1 = rect;
+        QRegion r2;
+        r2 = std::move(r1);
+        QVERIFY(r1.isNull());
+        QCOMPARE(r2, rect);
+    }
+
+    // move construction
+    {
+        QRegion r1 = rect;
+        QRegion r2 = std::move(r1);
+        QVERIFY(r1.isNull());
+        QCOMPARE(r2, rect);
+    }
+}
+
 void tst_QRegion::boundingRect()
 {
     {