* 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("getContentBounds", &Window::GetContentBounds)
      .SetMethod("setContentBounds", &Window::SetContentBounds)
      .SetMethod("getContentSize", &Window::GetContentSize)
      .SetMethod("setContentSize", &Window::SetContentSize)
      .SetMethod("setMinimumSize", &Window::SetMinimumSize)
      .SetMethod("getMinimumSize", &Window::GetMinimumSize)
      .SetMethod("setMaximumSize", &Window::SetMaximumSize)
      .SetMethod("getMaximumSize", &Window::GetMaximumSize)
      .SetMethod("setSheetOffset", &Window::SetSheetOffset)
      .SetMethod("setResizable", &Window::SetResizable)
      .SetMethod("isResizable", &Window::IsResizable)
      .SetMethod("setMovable", &Window::SetMovable)
      .SetMethod("isMovable", &Window::IsMovable)
      .SetMethod("setMinimizable", &Window::SetMinimizable)
      .SetMethod("isMinimizable", &Window::IsMinimizable)
      .SetMethod("setMaximizable", &Window::SetMaximizable)
      .SetMethod("isMaximizable", &Window::IsMaximizable)
      .SetMethod("setFullScreenable", &Window::SetFullScreenable)
      .SetMethod("isFullScreenable", &Window::IsFullScreenable)
      .SetMethod("setClosable", &Window::SetClosable)
      .SetMethod("isClosable", &Window::IsClosable)
      .SetMethod("setAlwaysOnTop", &Window::SetAlwaysOnTop)
      .SetMethod("isAlwaysOnTop", &Window::IsAlwaysOnTop)
      .SetMethod("center", &Window::Center)
      .SetMethod("setPosition", &Window::SetPosition)
      .SetMethod("getPosition", &Window::GetPosition)
      .SetMethod("setTitle", &Window::SetTitle)
      .SetMethod("getTitle", &Window::GetTitle)
      .SetMethod("flashFrame", &Window::FlashFrame)
      .SetMethod("setSkipTaskbar", &Window::SetSkipTaskbar)