* 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_window.cc
window_->SetEscapeTouchBarItem(item);
}
int32_t Window::ID() const {
  return weak_map_id();
}
v8::Local<v8::Value> Window::WebContents(v8::Isolate* isolate) {
  if (web_contents_.IsEmpty()) {
    return v8::Null(isolate);
  }
  return v8::Local<v8::Value>::New(isolate, web_contents_);
}
void Window::RemoveFromParentChildWindows() {
  if (parent_window_.IsEmpty())
    return;
  mate::Handle<Window> parent;
  if (!mate::ConvertFromV8(isolate(), GetParentWindow(), &parent))
    return;
  parent->child_windows_.Remove(ID());
}
void Window::BuildPrototype(v8::Isolate* isolate,
                            v8::Local<v8::FunctionTemplate> prototype) {
  prototype->SetClassName(mate::StringToV8(isolate, "BrowserWindow"));
  mate::ObjectTemplateBuilder(isolate, prototype->PrototypeTemplate())
      .MakeDestroyable()
      .SetMethod("close", &Window::Close)
      .SetMethod("focus", &Window::Focus)
      .SetMethod("blur", &Window::Blur)
      .SetMethod("isFocused", &Window::IsFocused)