* 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
#endif
      web_contents = content::WebContents::Create(params);
#if defined(ENABLE_OSR)
    }
  } else if (IsOffScreen()) {
    bool transparent = false;
    options.Get("transparent", &transparent);
    content::WebContents::CreateParams params(session->browser_context());
    auto* view = new OffScreenWebContentsView(transparent,
        base::Bind(&WebContents::OnPaint, base::Unretained(this)));
    params.view = view;
    params.delegate_view = view;
    web_contents = content::WebContents::Create(params);
    view->SetWebContents(web_contents);
#endif
  } else {
    content::WebContents::CreateParams params(session->browser_context());
    web_contents = content::WebContents::Create(params);
  }
  InitWithSessionAndOptions(isolate, web_contents, session, options);
}
void WebContents::InitZoomController(content::WebContents* web_contents,
                                     const mate::Dictionary& options) {
  WebContentsZoomController::CreateForWebContents(web_contents);
  zoom_controller_ = WebContentsZoomController::FromWebContents(web_contents);
  double zoom_factor;
  if (options.Get(options::kZoomFactor, &zoom_factor))
    zoom_controller_->SetDefaultZoomFactor(zoom_factor);
}
void WebContents::InitWithSessionAndOptions(v8::Isolate* isolate,