Description of problem:
I tried  to put a youtube video in full screen and webkitgtk stopped working, this was reproducible 2x in a row.
The video was The Weeknd - Lost in the fire.

Version-Release number of selected component:
webkit2gtk3-2.24.1-1.fc30

Additional info:
reporter:       libreport-2.10.0
backtrace_rating: 4
cmdline:        /usr/libexec/webkit2gtk-4.0/WebKitWebProcess 18 50
crash_function: WebCore::TreeScope::documentScope
executable:     /usr/libexec/webkit2gtk-4.0/WebKitWebProcess
journald_cursor: s=af3b477b89bf4dcda06f3b5049bf616f;i=ae00;b=9e815d4f228b4da2a2cddbdf64537280;m=1a048948;t=587d5c561e46c;x=cd9f9a984503ef1b
kernel:         5.0.9-301.fc30.x86_64
rootdir:        /
runlevel:       N 5
type:           CCpp
uid:            1000

Truncated backtrace:
Thread no. 1 (10 frames)
 #0 WebCore::TreeScope::documentScope at ../Source/WebCore/dom/TreeScope.h:73
 #1 WebCore::Node::document at ../Source/WebCore/dom/Node.h:361
 #2 WebKit::WebFullScreenManager::requestExitFullScreen at ../Source/WebKit/WebProcess/FullScreen/WebFullScreenManager.cpp:211
 #3 IPC::callMemberFunctionImpl<WebKit::WebFullScreenManager, void (WebKit::WebFullScreenManager::*)(), std::tuple<>>(WebKit::WebFullScreenManager*, void (WebKit::WebFullScreenManager::*)(), std::tuple<>&&, std::integer_sequence<unsigned long>) at ../Source/WebKit/Platform/IPC/HandleMessage.h:139
 #4 IPC::callMemberFunction<WebKit::WebFullScreenManager, void (WebKit::WebFullScreenManager::*)(), std::tuple<>, std::integer_sequence<unsigned long> >(std::tuple<>&&, WebKit::WebFullScreenManager*, void (WebKit::WebFullScreenManager::*)()) at ../Source/WebKit/Platform/IPC/HandleMessage.h:47
 #5 IPC::handleMessage<Messages::WebFullScreenManager::RequestExitFullScreen, WebKit::WebFullScreenManager, void (WebKit::WebFullScreenManager::*)()> at ../Source/WebKit/Platform/IPC/HandleMessage.h:147
 #6 WebKit::WebFullScreenManager::didReceiveWebFullScreenManagerMessage at DerivedSources/WebKit/WebFullScreenManagerMessageReceiver.cpp:43
 #7 IPC::MessageReceiverMap::dispatchMessage at ../Source/WebKit/Platform/IPC/MessageReceiverMap.cpp:123
 #8 WebKit::WebProcess::didReceiveMessage at ../Source/WebKit/Shared/AuxiliaryProcess.h:76
 #9 IPC::Connection::dispatchMessage at ../Source/WebKit/Platform/IPC/Connection.cpp:978