Add new property to QVideoSurfaceFormat.

The 'mirrored' property indicates the QVideoFrames need to be mirrored
along their vertical axis. This is typically needed for video frames
coming from a front camera on a mobile device.

This is implemented as a string-based property. In Qt 5.6, this should
be replaced by a new public function.

Change-Id: Ideb7de81e83f66826f4efb5f2951c4beec13546b
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>

src/qtmultimediaquicktools/qdeclarativevideooutput_render.cpp

@@ -255,6 +255,12 @@ void QDeclarativeVideoRendererBackend::updateGeometry()
         m_sourceTextureRect.setTop(m_sourceTextureRect.bottom());
         m_sourceTextureRect.setBottom(top);
     }
+
+    if (videoSurface()->surfaceFormat().property("mirrored").toBool()) {
+        qreal left = m_sourceTextureRect.left();
+        m_sourceTextureRect.setLeft(m_sourceTextureRect.right());
+        m_sourceTextureRect.setRight(left);
+    }
 }
 
 QSGNode *QDeclarativeVideoRendererBackend::updatePaintNode(QSGNode *oldNode,