* 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
*prevent_default = Emit("close");
}
void Window::WillDestroyNativeObject() {
  
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  for (v8::Local<v8::Value> value : child_windows_.Values(isolate())) {
    mate::Handle<Window> child;
    if (mate::ConvertFromV8(isolate(), value, &child))
      child->window_->CloseImmediately();
  }
}
void Window::OnWindowClosed() {
  api_web_contents_->DestroyWebContents(true );
  RemoveFromWeakMap();
  window_->RemoveObserver(this);
  
  
  MarkDestroyed();
  Emit("closed");
  RemoveFromParentChildWindows();
  ResetBrowserView();
  
  base::ThreadTaskRunnerHandle::Get()->PostTask(
      FROM_HERE, GetDestroyClosure());
}
void Window::OnWindowEndSession() {