* 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
return static_cast<AtomBrowserContext*>(web_contents()->GetBrowserContext());
}
void WebContents::OnRendererMessage(const base::string16& channel,
                                    const base::ListValue& args) {
  
  Emit(base::UTF16ToUTF8(channel), args);
}
void WebContents::OnRendererMessageSync(const base::string16& channel,
                                        const base::ListValue& args,
                                        IPC::Message* message) {
  
  EmitWithSender(base::UTF16ToUTF8(channel), web_contents(), message, args);
}
mate::Handle<WebContents> WebContents::CreateFrom(
    v8::Isolate* isolate, content::WebContents* web_contents) {
  
  auto existing = TrackableObject::FromWrappedClass(isolate, web_contents);
  if (existing)
    return mate::CreateHandle(isolate, static_cast<WebContents*>(existing));
  
  return mate::CreateHandle(isolate, new WebContents(isolate, web_contents,
        REMOTE));
}
mate::Handle<WebContents> WebContents::CreateFrom(