webbrowser app crashes saving an image in Xenial

[Víctor R. Ruiz]

Test case.
- Open webbrowser app
- Go to http://apod.nasa.gov/
- Long tap on the image.
- Tap to save the image.

Expected result.
- Image can be saved locally.

Actual result.
- Webbrowser app freezes and crashes.

current build number: 75
device name: frieza_arm64
channel: ubuntu-touch/staging/ubuntu

I see no webbrowser-app crash files in /var/crash. In the logs I see this (not sure whether it's related):

libpng error: Read Error
propsReply "An AppArmor policy prevents this sender from sending this message to this recipient; type=\"method_call\", sender=\":1.1498\" (uid=32011 pid=6867 comm=\"webbrowser-app \") interface=\"org.freedesktop.DBus.Properties\" member=\"GetAll\" error name=\"(unset)\" requested_reply=\"0\" destination=\"org.freedesktop.NetworkManager\" (uid=0 pid=953 comm=\"/usr/sbin/NetworkManager --no-daemon \")"
nmReply "An AppArmor policy prevents this sender from sending this message to this recipient; type=\"method_call\", sender=\":1.1498\" (uid=32011 pid=6867 comm=\"webbrowser-app \") interface=\"org.freedesktop.NetworkManager\" member=\"GetDevices\" error name=\"(unset)\" requested_reply=\"0\" destination=\"org.freedesktop.NetworkManager\" (uid=0 pid=953 comm=\"/usr/sbin/NetworkManager --no-daemon \")"
"Object path cannot be empty"
[1104/161741:ERROR:object_proxy.cc(583)] Failed to call method: org.freedesktop.ScreenSaver.Inhibit: object_path= /org/freedesktop/ScreenSaver: org.freedesktop.DBus.Error.AccessDenied: An AppArmor policy prevents this sender from sending this message to this recipient; type="method_call", sender=":1.7787" (uid=32011 pid=6867 comm="webbrowser-app ") interface="org.freedesktop.ScreenSaver" member="Inhibit" error name="(unset)" requested_reply="0" destination="org.freedesktop.ScreenSaver" (uid=32011 pid=2691 comm="unity8 --mode=full-greeter ")

[Olivier Tilloy (osomon)]

(gdb) bt
#0 0x0000007f730aad58 in QDBusAbstractInterface::asyncCallWithArgumentList(QString const&, QList<QVariant> const&) ()
   from /usr/lib/aarch64-linux-gnu/libQt5DBus.so.5
#1 0x0000007f72dfdac8 in ?? ()
   from /usr/lib/aarch64-linux-gnu/libubuntu-download-manager-client.so.1
#2 0x0000007f40348174 in Ubuntu::DownloadManager::SingleDownload::setAllowMobileDownload(bool) ()
   from /usr/lib/aarch64-linux-gnu/qt5/qml/Ubuntu/DownloadManager/libUbuntuDownloadManager.so
#3 0x0000007f40349f4c in Ubuntu::DownloadManager::SingleDownload::bindDownload(Ubuntu::DownloadManager::Download*) ()
   from /usr/lib/aarch64-linux-gnu/qt5/qml/Ubuntu/DownloadManager/libUbuntuDownloadManager.so
#4 0x0000007f7889a58c in QMetaObject::activate(QObject*, int, int, void**) ()
   from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#5 0x0000007f72e26b44 in Ubuntu::DownloadManager::Manager::downloadCreated(Ubuntu::DownloadManager::Download*) ()
   from /usr/lib/aarch64-linux-gnu/libubuntu-download-manager-client.so.1
#6 0x0000007f72e225b4 in ?? ()
   from /usr/lib/aarch64-linux-gnu/libubuntu-download-manager-client.so.1
#7 0x0000007f7889a58c in QMetaObject::activate(QObject*, int, int, void**) ()
   from /usr/lib/aarch64-linux-gnu/libQt5Core.so.5
#8 0x0000007f730e552c in QDBusPendingCallWatcher::finished(QDBusPendingCallWatcher*) () from /usr/lib/aarch64-linux-gnu/libQt5DBus.so.5
#9 0x0000007f730e5658 in ?? () from /usr/lib/aarch64-linux-gnu/libQt5DBus.so.5
#10 0x0000000012cfee30 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)