Bug 485579. Fix possible crash when closing tabs using cairo-qt. r=vlad, a=beltzner

widget/src/qt/mozqwidget.cpp

@@ -10,6 +10,12 @@ MozQWidget::MozQWidget(nsWindow *receiver, QWidget *parent,
     setAttribute(Qt::WA_QuitOnClose, false);
 }
 
+MozQWidget::~MozQWidget()
+{
+    if (mReceiver)
+        mReceiver->QWidgetDestroyed();
+}
+
 bool MozQWidget::event(QEvent *e)
 {
     nsEventStatus status = nsEventStatus_eIgnore;

widget/src/qt/mozqwidget.h

@@ -14,6 +14,8 @@ public:
     MozQWidget(nsWindow* receiver, QWidget *parent,
                const char *name, int f);
 
+    ~MozQWidget();
+
     /**
      * Mozilla helper.
      */

widget/src/qt/nsWindow.cpp

@@ -109,6 +109,8 @@
 #include "qx11info_x11.h"
 #endif
 
+#include <QtCore/QDebug>
+
 #include <execinfo.h>
 
 #include "mozqwidget.h"
@@ -316,6 +318,7 @@ nsWindow::Destroy(void)
         mMozQWidget->deleteLater();
     }
 
+    mMozQWidget = nsnull;
     mDrawingArea = nsnull;
 
     OnDestroy();
@@ -1968,6 +1971,12 @@ nsWindow::ConvertBorderStyles(nsBorderStyle aStyle)
     return w;
 }
 
+void nsWindow::QWidgetDestroyed()
+{
+    mDrawingArea = nsnull;
+    mMozQWidget = nsnull;
+}
+
 NS_IMETHODIMP
 nsWindow::MakeFullScreen(PRBool aFullScreen)
 {

widget/src/qt/nsWindow.h

@@ -208,6 +208,8 @@ public:
     void               LoseFocus();
     qint32             ConvertBorderStyles(nsBorderStyle aStyle);
 
+    void               QWidgetDestroyed();
+
 
     /***** from CommonWidget *****/