* 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::IsVisibleOnAllWorkspaces)
#if defined(OS_MACOSX)
      .SetMethod("setAutoHideCursor", &Window::SetAutoHideCursor)
      .SetMethod("mergeAllWindows", &Window::MergeAllWindows)
      .SetMethod("selectPreviousTab", &Window::SelectPreviousTab)
      .SetMethod("selectNextTab", &Window::SelectNextTab)
      .SetMethod("moveTabToNewWindow", &Window::MoveTabToNewWindow)
      .SetMethod("toggleTabBar", &Window::ToggleTabBar)
      .SetMethod("addTabbedWindow", &Window::AddTabbedWindow)
#endif
      .SetMethod("setVibrancy", &Window::SetVibrancy)
      .SetMethod("_setTouchBarItems", &Window::SetTouchBar)
      .SetMethod("_refreshTouchBarItem", &Window::RefreshTouchBarItem)
      .SetMethod("_setEscapeTouchBarItem", &Window::SetEscapeTouchBarItem)
#if defined(OS_WIN)
      .SetMethod("hookWindowMessage", &Window::HookWindowMessage)
      .SetMethod("isWindowMessageHooked", &Window::IsWindowMessageHooked)
      .SetMethod("unhookWindowMessage", &Window::UnhookWindowMessage)
      .SetMethod("unhookAllWindowMessages", &Window::UnhookAllWindowMessages)
      .SetMethod("setThumbnailClip", &Window::SetThumbnailClip)
      .SetMethod("setThumbnailToolTip", &Window::SetThumbnailToolTip)
      .SetMethod("setAppDetails", &Window::SetAppDetails)
#endif
#if defined(TOOLKIT_VIEWS)
      .SetMethod("setIcon", &Window::SetIcon)
#endif
      .SetProperty("id", &Window::ID)
      .SetProperty("webContents", &Window::WebContents);
}
v8::Local<v8::Value> Window::From(v8::Isolate* isolate,