I got this when WebContent crashed. Memory usage was at about half (256 MB)
Trace:

[FinalizerTask(4:4)]: ASSERTION FAILED: m_has_value
[FinalizerTask(4:4)]: ../.././AK/Optional.h:132 in T& AK::Optional<T>::value() [with T = Kernel::UserOrKernelBuffer]
[FinalizerTask(4:4)]: KERNEL PANIC! :^(
[FinalizerTask(4:4)]: Aborted
[FinalizerTask(4:4)]: at ../../Kernel/Arch/x86/common/CPU.cpp:29 in void abort()
[FinalizerTask(4:4)]: Kernel + 0x00848ad2  Kernel::__panic(char const*, unsigned int, char const*) +0x68
[FinalizerTask(4:4)]: Kernel + 0x00c1f7fe  abort.localalias +0x1f0
[FinalizerTask(4:4)]: Kernel + 0x00c1f88f  void AK::critical_dmesgln<char const*>(AK::Format::Detail::CheckedFormatString<AK::Detail::__IdentityType<char const*>::Type>&&, char const* const&) +0x0
[FinalizerTask(4:4)]: Kernel + 0x001fb6cd  Kernel::CoreDump::write_regions() [clone .localalias] +0x218f
[FinalizerTask(4:4)]: Kernel + 0x0020a535  Kernel::CoreDump::write() +0x83f
[FinalizerTask(4:4)]: Kernel + 0x0087695f  Kernel::Process::dump_core() [clone .localalias] +0x6ed
[FinalizerTask(4:4)]: Kernel + 0x0087fab7  Kernel::Process::finalize() +0x287
[FinalizerTask(4:4)]: Kernel + 0x00b645e0  Kernel::Thread::drop_thread_count(bool) [clone .localalias] +0x322
[FinalizerTask(4:4)]: Kernel + 0x00b803de  Kernel::Thread::finalize() [clone .localalias] +0x63a
[FinalizerTask(4:4)]: Kernel + 0x00b8125f  Kernel::Thread::finalize_dying_threads() +0x717
[FinalizerTask(4:4)]: Kernel + 0x00b582ea  Kernel::finalizer_task(void*) +0x13b
[FinalizerTask(4:4)]: Kernel + 0x00c296a8  exit_kernel_thread +0x0