* 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
content::WebContents* source,
    const content::NativeWebKeyboardEvent& event) {
  if (event.GetType() == blink::WebInputEvent::Type::kRawKeyDown ||
      event.GetType() == blink::WebInputEvent::Type::kKeyUp) {
    bool prevent_default = Emit("before-input-event", event);
    if (prevent_default) {
      return content::KeyboardEventProcessingResult::HANDLED;
    }
  }
  return content::KeyboardEventProcessingResult::NOT_HANDLED;
}
void WebContents::EnterFullscreenModeForTab(content::WebContents* source,
                                            const GURL& origin) {
  auto permission_helper =
      WebContentsPermissionHelper::FromWebContents(source);
  auto callback = base::Bind(&WebContents::OnEnterFullscreenModeForTab,
                             base::Unretained(this), source, origin);
  permission_helper->RequestFullscreenPermission(callback);
}
void WebContents::OnEnterFullscreenModeForTab(content::WebContents* source,
                                              const GURL& origin,
                                              bool allowed) {
  if (!allowed)
    return;
  CommonWebContentsDelegate::EnterFullscreenModeForTab(source, origin);
  Emit("enter-html-full-screen");
}
void WebContents::ExitFullscreenModeForTab(content::WebContents* source) {