* 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
NativeWindow* native_window) {
  auto existing = TrackableObject::FromWrappedClass(isolate, native_window);
  if (existing)
    return existing->GetWrapper();
  else
    return v8::Null(isolate);
}
}  
}  
namespace {
using atom::api::Window;
void Initialize(v8::Local<v8::Object> exports, v8::Local<v8::Value> unused,
                v8::Local<v8::Context> context, void* priv) {
  v8::Isolate* isolate = context->GetIsolate();
  Window::SetConstructor(isolate, base::Bind(&Window::New));
  mate::Dictionary browser_window(
      isolate, Window::GetConstructor(isolate)->GetFunction());
  browser_window.SetMethod("fromId",
                           &mate::TrackableObject<Window>::FromWeakMapID);
  browser_window.SetMethod("getAllWindows",
                           &mate::TrackableObject<Window>::GetAll);
  mate::Dictionary dict(isolate, exports);
  dict.Set("BrowserWindow", browser_window);
}
}  
NODE_MODULE_CONTEXT_AWARE_BUILTIN(atom_browser_window, Initialize)