* Electron version: 1.6.15
* Operating system: Linux

### Expected behavior

Open a `BrowserWindow` with passed options

### Actual behavior

  - Usually a Segmentation fault.
  - Sometimes `[12843:0100/000000.043847:FATAL:zygote_linux.cc(479)] Failed to synchronise with parent zygote process`
  - Sometimes `[12819:0100/000000.719122:FATAL:zygote_linux.cc(509)] Check failed: len > 0 (0 vs. 0)`

### How to reproduce

I'm still working on making a smaller reproduction case. The issue goes away with small tweaks.

1. Starting from https://github.com/daurnimator/fengari-electron-example
2. Modify main.lua to contain:
```lua
local js = require "js"
local electron = require "electron"

electron.app:on("ready", function()
	local win = js.new(electron.BrowserWindow, js.createproxy({
		backgroundColor = '#2e2c29';
	}, "object"))
	win:loadURL("https://fengari.io")
end)
```

atom/browser/api/atom_api_web_contents.cc
const gfx::RectF& bounds,
                                    const std::vector<base::string16>& values,
                                    const std::vector<base::string16>& labels) {
  auto relay = NativeWindowRelay::FromWebContents(web_contents());
  if (relay) {
    relay->window->ShowAutofillPopup(
        frame_host, web_contents(), bounds, values, labels);
  }
}
bool WebContents::OnMessageReceived(const IPC::Message& message) {
  bool handled = true;
  IPC_BEGIN_MESSAGE_MAP(WebContents, message)
    IPC_MESSAGE_HANDLER(AtomViewHostMsg_Message, OnRendererMessage)
    IPC_MESSAGE_HANDLER_DELAY_REPLY(AtomViewHostMsg_Message_Sync,
                                    OnRendererMessageSync)
    IPC_MESSAGE_HANDLER_DELAY_REPLY(AtomViewHostMsg_SetTemporaryZoomLevel,
                                    OnSetTemporaryZoomLevel)
    IPC_MESSAGE_HANDLER_DELAY_REPLY(AtomViewHostMsg_GetZoomLevel,
                                    OnGetZoomLevel)
    IPC_MESSAGE_HANDLER_CODE(ViewHostMsg_SetCursor, OnCursorChange,
      handled = false)
    IPC_MESSAGE_UNHANDLED(handled = false)
  IPC_END_MESSAGE_MAP()
  return handled;
}
bool WebContents::OnMessageReceived(const IPC::Message& message,