* Electron version: 1.7.1
* Operating system: Windows / Mac

### Expected behavior
no crash on quit

### Actual behavior
Crash on app quit

```
Thread 23 Crashed:: Chrome_IOThread
0   com.github.electron.framework 	0x000000010e3761f2 std::__1::__tree<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::less<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > >::destroy(std::__1::__tree_node<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, void*>*) + 18 (__tree:1828)
1   com.github.electron.framework 	0x000000010dac0047 std::__1::__tree<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::less<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > >::clear() + 23 (__tree:1831)
2   com.github.electron.framework 	0x000000010dabffed atom::AtomCTDelegate::ClearCTExcludedHostsList() + 13 (atom_ct_delegate.cc:23)
3   com.github.electron.framework 	0x000000010dabe69a atom::AtomCertVerifier::Verify(net::CertVerifier::RequestParams const&, net::CRLSet*, net::CertVerifyResult*, base::Callback<void (int), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&, std::__1::unique_ptr<net::CertVerifier::Request, std::__1::default_delete<net::CertVerifier::Request> >*, net::NetLogWithSource const&) + 58 (atom_cert_verifier.cc:170)
4   com.github.electron.framework 	0x000000010f5104fa net::SSLClientSocketImpl::DoVerifyCert(int) + 586 (ssl_client_socket_impl.cc:1273)
5   com.github.electron.framework 	0x000000010f50e3a0 net::SSLClientSocketImpl::DoHandshakeLoop(int) + 160 (ssl_client_socket_impl.cc:1404)
6   com.github.electron.framework 	0x000000010f50ffd5 net::SSLClientSocketImpl::OnHandshakeIOComplete(int) + 21 (ssl_client_socket_impl.cc:1370)
7   com.github.electron.framework 	0x000000010f5192e3 net::TCPClientSocket::DidCompleteRead(base::Callback<void (int), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&, int) + 115 (tcp_client_socket.cc:357)
8   com.github.electron.framework 	0x000000010f51c09f net::TCPSocketPosix::ReadCompleted(scoped_refptr<net::IOBuffer> const&, base::Callback<void (int), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&, int) + 31 (tcp_socket_posix.cc:590)
9   com.github.electron.framework 	0x000000010f4d972f net::SocketPosix::ReadCompleted() + 207 (socket_posix.cc:465)
10  com.github.electron.framework 	0x000000010f4d9626 net::SocketPosix::OnFileCanReadWithoutBlocking(int) + 310 (trace_event.h:1033)
11  com.github.electron.framework 	0x000000010dc4c8b7 base::MessagePumpLibevent::OnLibeventNotification(int, short, void*) + 215 (message_pump_libevent.cc:341)
12  com.github.electron.framework 	0x000000010dcb7e85 event_base_loop + 1205 (event.c:521)
13  com.github.electron.framework 	0x000000010dc4cadf base::MessagePumpLibevent::Run(base::MessagePump::Delegate*) + 127 (message_pump_libevent.cc:224)
14  com.github.electron.framework 	0x000000010dc498ee base::MessageLoop::RunHandler() + 94 (message_loop.cc:388)
15  com.github.electron.framework 	0x000000010dc634f3 base::RunLoop::Run() + 115 (run_loop.cc:38)
16  com.github.electron.framework 	0x000000010ded33d8 content::BrowserThreadImpl::IOThreadRun(base::RunLoop*) + 24 (browser_thread_impl.cc:278)
17  com.github.electron.framework 	0x000000010ded3566 content::BrowserThreadImpl::Run(base::RunLoop*) + 294 (browser_thread_impl.cc:312)
18  com.github.electron.framework 	0x000000010dc83c59 base::Thread::ThreadMain() + 393 (thread.cc:336)
19  com.github.electron.framework 	0x000000010dc57a87 base::(anonymous namespace)::ThreadFunc(void*) + 87 (platform_thread_posix.cc:73)
20  libsystem_pthread.dylib       	0x00007fff8344c99d _pthread_body + 131
21  libsystem_pthread.dylib       	0x00007fff8344c91a _pthread_start + 168
22  libsystem_pthread.dylib       	0x00007fff8344a351 thread_start + 13
```

### How to reproduce
No consistent repro. May be happening after #7651

cc: @kevinsawicki @deepak1556 
brightray/browser/url_request_context_getter.cc
URLRequestContextGetter::Delegate::CreateHttpCacheBackendFactory(
    const base::FilePath& base_path) {
  auto command_line = base::CommandLine::ForCurrentProcess();
  int max_size = 0;
  base::StringToInt(command_line->GetSwitchValueASCII(switches::kDiskCacheSize),
                    &max_size);
  base::FilePath cache_path = base_path.Append(FILE_PATH_LITERAL("Cache"));
  return new net::HttpCache::DefaultBackend(
      net::DISK_CACHE,
      net::CACHE_BACKEND_DEFAULT,
      cache_path,
      max_size,
      BrowserThread::GetTaskRunnerForThread(BrowserThread::CACHE));
}
std::unique_ptr<net::CertVerifier>