* 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_->SetMaximizable(maximizable);
}
bool Window::IsMaximizable() {
  return window_->IsMaximizable();
}
void Window::SetFullScreenable(bool fullscreenable) {
  window_->SetFullScreenable(fullscreenable);
}
bool Window::IsFullScreenable() {
  return window_->IsFullScreenable();
}
void Window::SetClosable(bool closable) {
  window_->SetClosable(closable);
}
bool Window::IsClosable() {
  return window_->IsClosable();
}
void Window::SetAlwaysOnTop(bool top, mate::Arguments* args) {
  std::string level = "floating";
  int relativeLevel = 0;
  std::string error;
  args->GetNext(&level);
  args->GetNext(&relativeLevel);
  window_->SetAlwaysOnTop(top, level, relativeLevel, &error);
  if (!error.empty()) {
    args->ThrowError(error);
  }
}
bool Window::IsAlwaysOnTop() {