* 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("setSimpleFullScreen", &Window::SetSimpleFullScreen)
      .SetMethod("isSimpleFullScreen", &Window::IsSimpleFullScreen)
      .SetMethod("setKiosk", &Window::SetKiosk)
      .SetMethod("isKiosk", &Window::IsKiosk)
      .SetMethod("setBackgroundColor", &Window::SetBackgroundColor)
      .SetMethod("setHasShadow", &Window::SetHasShadow)
      .SetMethod("hasShadow", &Window::HasShadow)
      .SetMethod("setOpacity", &Window::SetOpacity)
      .SetMethod("getOpacity", &Window::GetOpacity)
      .SetMethod("setRepresentedFilename", &Window::SetRepresentedFilename)
      .SetMethod("getRepresentedFilename", &Window::GetRepresentedFilename)
      .SetMethod("setDocumentEdited", &Window::SetDocumentEdited)
      .SetMethod("isDocumentEdited", &Window::IsDocumentEdited)
      .SetMethod("setIgnoreMouseEvents", &Window::SetIgnoreMouseEvents)
      .SetMethod("setContentProtection", &Window::SetContentProtection)
      .SetMethod("setFocusable", &Window::SetFocusable)
      .SetMethod("focusOnWebView", &Window::FocusOnWebView)
      .SetMethod("blurWebView", &Window::BlurWebView)
      .SetMethod("isWebViewFocused", &Window::IsWebViewFocused)
      .SetMethod("setProgressBar", &Window::SetProgressBar)
      .SetMethod("setOverlayIcon", &Window::SetOverlayIcon)
      .SetMethod("setThumbarButtons", &Window::SetThumbarButtons)
      .SetMethod("setMenu", &Window::SetMenu)
      .SetMethod("setAutoHideMenuBar", &Window::SetAutoHideMenuBar)
      .SetMethod("isMenuBarAutoHide", &Window::IsMenuBarAutoHide)
      .SetMethod("setMenuBarVisibility", &Window::SetMenuBarVisibility)
      .SetMethod("isMenuBarVisible", &Window::IsMenuBarVisible)
      .SetMethod("setVisibleOnAllWorkspaces",
                 &Window::SetVisibleOnAllWorkspaces)
      .SetMethod("isVisibleOnAllWorkspaces",