* 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
std::vector<int> result(2);
  gfx::Size size = window_->GetMaximumSize();
  result[0] = size.width();
  result[1] = size.height();
  return result;
}
void Window::SetSheetOffset(double offsetY, mate::Arguments* args) {
  double offsetX = 0.0;
  args->GetNext(&offsetX);
  window_->SetSheetOffset(offsetX, offsetY);
}
void Window::SetResizable(bool resizable) {
  window_->SetResizable(resizable);
}
bool Window::IsResizable() {
  return window_->IsResizable();
}
void Window::SetMovable(bool movable) {
  window_->SetMovable(movable);
}
bool Window::IsMovable() {
  return window_->IsMovable();
}
void Window::SetMinimizable(bool minimizable) {
  window_->SetMinimizable(minimizable);
}
bool Window::IsMinimizable() {
  return window_->IsMinimizable();
}
void Window::SetMaximizable(bool maximizable) {