* 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_web_contents.cc
if (owner_window)
      SetOwnerWindow(owner_window);
  }
  Init(isolate);
  AttachAsUserData(web_contents);
}
WebContents::~WebContents() {
  
  if (managed_web_contents()) {
    
    
    if (type_ == WEB_VIEW)
      guest_delegate_->Destroy();
    RenderViewDeleted(web_contents()->GetRenderViewHost());
    if (type_ == WEB_VIEW) {
      DestroyWebContents(false );
    } else {
      if (type_ == BROWSER_WINDOW && owner_window()) {
        owner_window()->CloseContents(nullptr);
      } else {
        DestroyWebContents(true );
      }
      
      
      
      WebContentsDestroyed();
    }
  }
}
void WebContents::DestroyWebContents(bool async) {