#0  content::RenderProcessHostImpl::Cleanup ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/renderer_host/render_process_host_impl.cc:3345
#1  0x00007fffe059df97 in content::RenderProcessHostImpl::RemoveRoute ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/renderer_host/render_process_host_impl.cc:2442
#2  0x00007fffe05a9f1c in content::RenderViewHostImpl::~RenderViewHostImpl ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/renderer_host/render_view_host_impl.cc:274
#3  0x00007fffe05aa151 in content::RenderViewHostImpl::~RenderViewHostImpl ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/renderer_host/render_view_host_impl.cc:280
#4  0x00007fffe05a9912 in content::RenderViewHostImpl::ShutdownAndDestroy ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/renderer_host/render_view_host_impl.cc:810
#5  0x00007fffe0399187 in content::FrameTree::ReleaseRenderViewHostRef ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/frame_host/frame_tree.cc:407
#6  0x00007fffe03dacb1 in content::RenderFrameHostImpl::~RenderFrameHostImpl ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/frame_host/render_frame_host_impl.cc:721
#7  0x00007fffe03db7a1 in content::RenderFrameHostImpl::~RenderFrameHostImpl ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/frame_host/render_frame_host_impl.cc:735
#8  0x00007fffe03ecf00 in std::default_delete<content::RenderFrameHostImpl>::operator() () at /usr/include/c++/7/bits/unique_ptr.h:78
#9  std::unique_ptr<content::RenderFrameHostImpl, std::default_delete<content::RenderFrameHostImpl> >::~unique_ptr ()
    at /usr/include/c++/7/bits/unique_ptr.h:268
#10 content::RenderFrameHostManager::~RenderFrameHostManager ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/frame_host/render_frame_host_manager.cc:96
#11 0x00007fffe039d35b in content::FrameTreeNode::~FrameTreeNode ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/frame_host/frame_tree_node.cc:138
#12 0x00007fffe039777b in content::FrameTree::~FrameTree ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/frame_host/frame_tree.cc:119
#13 0x00007fffe06cc77c in content::WebContentsImpl::~WebContentsImpl ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/web_contents/web_contents_impl.cc:584
#14 0x00007fffe06cca91 in content::WebContentsImpl::~WebContentsImpl ()
    at ../../../../../qtwebengine/src/3rdparty/chromium/content/browser/web_contents/web_contents_impl.cc:689
#15 0x00007fffded49c67 in std::default_delete<content::WebContents>::operator() (this=<optimized out>, __ptr=<optimized out>)
    at /usr/include/c++/7/bits/unique_ptr.h:78
#16 std::unique_ptr<content::WebContents, std::default_delete<content::WebContents> >::~unique_ptr (this=0x555555f439f8,
    __in_chrg=<optimized out>) at /usr/include/c++/7/bits/unique_ptr.h:268
#17 QtWebEngineCore::WebContentsAdapter::~WebContentsAdapter (this=0x555555f439e0, __in_chrg=<optimized out>)
    at /src/qt5/qtwebengine/src/core/web_contents_adapter.cpp:427
#18 0x00007fffe61ffbd2 in QtSharedPointer::ExternalRefCountData::destroy (this=0x555555f439d0)
    at /src/qt5/build9/qtbase/include/QtCore/../../../../qtbase/src/corelib/tools/qsharedpointer_impl.h:157
#19 QSharedPointer<QtWebEngineCore::WebContentsAdapter>::deref (dd=0x555555f439d0)
    at /src/qt5/build9/qtbase/include/QtCore/../../../../qtbase/src/corelib/tools/qsharedpointer_impl.h:465
#20 QSharedPointer<QtWebEngineCore::WebContentsAdapter>::deref (this=0x555555e12920)
    at /src/qt5/build9/qtbase/include/QtCore/../../../../qtbase/src/corelib/tools/qsharedpointer_impl.h:460
#21 QSharedPointer<QtWebEngineCore::WebContentsAdapter>::~QSharedPointer (this=0x555555e12920, __in_chrg=<optimized out>)
    at /src/qt5/build9/qtbase/include/QtCore/../../../../qtbase/src/corelib/tools/qsharedpointer_impl.h:315
#22 QWebEnginePagePrivate::~QWebEnginePagePrivate (this=0x555555e12910, __in_chrg=<optimized out>)
    at /src/qt5/qtwebengine/src/webenginewidgets/api/qwebenginepage.cpp:261
#23 0x00007fffe61ffc49 in QWebEnginePagePrivate::~QWebEnginePagePrivate (this=0x555555e12910, __in_chrg=<optimized out>)
    at /src/qt5/qtwebengine/src/webenginewidgets/api/qwebenginepage.cpp:265
#24 0x00007fffe61fb7a2 in QScopedPointerDeleter<QWebEnginePagePrivate>::cleanup (pointer=<optimized out>)
    at /src/qt5/build9/qtbase/include/QtCore/../../../../qtbase/src/corelib/tools/qscopedpointer.h:60
#25 QScopedPointer<QWebEnginePagePrivate, QScopedPointerDeleter<QWebEnginePagePrivate> >::~QScopedPointer (this=0x555555e14e60,
    __in_chrg=<optimized out>) at /src/qt5/build9/qtbase/include/QtCore/../../../../qtbase/src/corelib/tools/qscopedpointer.h:107
#26 QWebEnginePage::~QWebEnginePage (this=0x555555e14e50, __in_chrg=<optimized out>)
    at /src/qt5/qtwebengine/src/webenginewidgets/api/qwebenginepage.cpp:900
#27 0x00007ffff0d061be in WebEngineViewer::WebEnginePage::~WebEnginePage() ()
   from /opt/kde5/lib/x86_64-linux-gnu/libKF5WebEngineViewer.so.5
#28 0x00007ffff22dfce6 in MessageViewer::MailWebEnginePage::~MailWebEnginePage() ()
   from /opt/kde5/lib/x86_64-linux-gnu/libKF5MessageViewer.so.5
#29 0x00007ffff22dfd02 in MessageViewer::MailWebEnginePage::~MailWebEnginePage() ()
   from /opt/kde5/lib/x86_64-linux-gnu/libKF5MessageViewer.so.5
#30 0x00007ffff5ca232b in QObjectPrivate::deleteChildren (this=this@entry=0x555555de6150)
    at /src/qt5/qtbase/src/corelib/kernel/qobject.cpp:2004
#31 0x00007ffff671f884 in QWidget::~QWidget (this=0x555555e54d40, __in_chrg=<optimized out>)
    at /src/qt5/qtbase/src/widgets/kernel/qwidget.cpp:1705
#32 0x00007ffff0d089f1 in WebEngineViewer::WebEngineView::~WebEngineView() ()