* 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
return window_->SetContentProtection(enable);
}
void Window::SetFocusable(bool focusable) {
  return window_->SetFocusable(focusable);
}
void Window::SetProgressBar(double progress, mate::Arguments* args) {
  mate::Dictionary options;
  std::string mode;
  NativeWindow::ProgressState state = NativeWindow::PROGRESS_NORMAL;
  args->GetNext(&options) && options.Get("mode", &mode);
  if (mode == "error") {
    state = NativeWindow::PROGRESS_ERROR;
  } else if (mode == "paused") {
    state = NativeWindow::PROGRESS_PAUSED;
  } else if (mode == "indeterminate") {
    state = NativeWindow::PROGRESS_INDETERMINATE;
  } else if (mode == "none") {
    state = NativeWindow::PROGRESS_NONE;
  }
  window_->SetProgressBar(progress, state);
}
void Window::SetOverlayIcon(const gfx::Image& overlay,
                            const std::string& description) {
  window_->SetOverlayIcon(overlay, description);
}
bool Window::SetThumbarButtons(mate::Arguments* args) {