* 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
const gfx::Rect& pos) {
  Emit("move", pos);
}
void WebContents::CloseContents(content::WebContents* source) {
  Emit("close");
  if ((type_ == BROWSER_WINDOW || type_ == OFF_SCREEN) && owner_window())
    owner_window()->CloseContents(source);
}
void WebContents::ActivateContents(content::WebContents* source) {
  Emit("activate");
}
void WebContents::UpdateTargetURL(content::WebContents* source,
                                  const GURL& url) {
  Emit("update-target-url", url);
}
bool WebContents::IsPopupOrPanel(const content::WebContents* source) const {
  return type_ == BROWSER_WINDOW;
}
void WebContents::HandleKeyboardEvent(
    content::WebContents* source,
    const content::NativeWebKeyboardEvent& event) {
  if (type_ == WEB_VIEW && embedder_) {
    
    embedder_->HandleKeyboardEvent(source, event);
  } else {
    
    CommonWebContentsDelegate::HandleKeyboardEvent(source, event);
  }
}
content::KeyboardEventProcessingResult WebContents::PreHandleKeyboardEvent(