OpenGL: destroy QGLContext allocated by QGLContext::fromOpenGLContext

QGLContext already uses ownContext to identify when it "owns" QOpenGLContext
and will delete QOpenGLContext when needed.  In the other way
QGLContext::fromOpenGLContext creates a QGLContext for QOpenGLContext, and is
now using qGLContextDeleteFunction to identify if QOpenGLContext "owns"
QGLContext by QGLContext only passing a delete function when QOpenGLContext
should delete QGLContext, and by QOpenGLContext calling deleteQGLContext() from
destory() to do the destruction avoiding the previous leak and sometimes crash
on exit.

Change-Id: I65e791776e99b456e4d0c70fc5b5cdb33c975893
Task-number: QTBUG-40286
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>

src/gui/kernel/qopenglcontext.cpp

@@ -538,6 +538,7 @@ bool QOpenGLContext::create()
 */
 void QOpenGLContext::destroy()
 {
+    deleteQGLContext();
     Q_D(QOpenGLContext);
     if (d->platformGLContext)
         emit aboutToBeDestroyed();
@@ -984,6 +985,9 @@ void *QOpenGLContext::qGLContextHandle() const
 }
 
 /*!
+    internal: If the delete function is specified QOpenGLContext "owns"
+    the passed context handle and will use the delete function to destroy it.
+
     \internal
 */
 void QOpenGLContext::setQGLContextHandle(void *handle,void (*qGLContextDeleteFunction)(void *))

src/opengl/qgl_p.h

@@ -242,6 +242,7 @@ public:
     void swapRegion(const QRegion &region);
 
     QOpenGLContext *guiGlContext;
+    // true if QGLContext owns the QOpenGLContext (for who deletes who)
     bool ownContext;
 
     void setupSharing();

src/opengl/qgl_qpa.cpp

@@ -135,7 +135,7 @@ bool QGLFormat::hasOpenGL()
             ->hasCapability(QPlatformIntegration::OpenGL);
 }
 
-void qDeleteQGLContext(void *handle)
+static void qDeleteQGLContext(void *handle)
 {
     QGLContext *context = static_cast<QGLContext *>(handle);
     delete context;
@@ -177,7 +177,7 @@ bool QGLContext::chooseContext(const QGLContext* shareContext)
         d->valid = d->guiGlContext->create();
 
         if (d->valid)
-            d->guiGlContext->setQGLContextHandle(this,qDeleteQGLContext);
+            d->guiGlContext->setQGLContextHandle(this, 0);
 
         d->glFormat = QGLFormat::fromSurfaceFormat(d->guiGlContext->format());
         d->setupSharing();