* 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
.SetMethod("show", &Window::Show)
      .SetMethod("showInactive", &Window::ShowInactive)
      .SetMethod("hide", &Window::Hide)
      .SetMethod("isVisible", &Window::IsVisible)
      .SetMethod("isEnabled", &Window::IsEnabled)
      .SetMethod("setEnabled", & Window::SetEnabled)
      .SetMethod("maximize", &Window::Maximize)
      .SetMethod("unmaximize", &Window::Unmaximize)
      .SetMethod("isMaximized", &Window::IsMaximized)
      .SetMethod("minimize", &Window::Minimize)
      .SetMethod("restore", &Window::Restore)
      .SetMethod("isMinimized", &Window::IsMinimized)
      .SetMethod("setFullScreen", &Window::SetFullScreen)
      .SetMethod("isFullScreen", &Window::IsFullscreen)
      .SetMethod("setAspectRatio", &Window::SetAspectRatio)
      .SetMethod("previewFile", &Window::PreviewFile)
      .SetMethod("closeFilePreview", &Window::CloseFilePreview)
#if !defined(OS_WIN)
      .SetMethod("setParentWindow", &Window::SetParentWindow)
#endif
      .SetMethod("getParentWindow", &Window::GetParentWindow)
      .SetMethod("getChildWindows", &Window::GetChildWindows)
      .SetMethod("getBrowserView", &Window::GetBrowserView)
      .SetMethod("setBrowserView", &Window::SetBrowserView)
      .SetMethod("isModal", &Window::IsModal)
      .SetMethod("getNativeWindowHandle", &Window::GetNativeWindowHandle)
      .SetMethod("getBounds", &Window::GetBounds)
      .SetMethod("setBounds", &Window::SetBounds)
      .SetMethod("getSize", &Window::GetSize)
      .SetMethod("setSize", &Window::SetSize)