* 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 (mate::ConvertFromV8(isolate, input_event, &keyboard_event)) {
      view->ProcessKeyboardEvent(keyboard_event, ui::LatencyInfo());
      return;
    }
  } else if (type == blink::WebInputEvent::kMouseWheel) {
    blink::WebMouseWheelEvent mouse_wheel_event;
    if (mate::ConvertFromV8(isolate, input_event, &mouse_wheel_event)) {
      view->ProcessMouseWheelEvent(mouse_wheel_event, ui::LatencyInfo());
      return;
    }
  }
  isolate->ThrowException(v8::Exception::Error(mate::StringToV8(
      isolate, "Invalid event object")));
}
void WebContents::BeginFrameSubscription(mate::Arguments* args) {
  bool only_dirty = false;
  FrameSubscriber::FrameCaptureCallback callback;
  args->GetNext(&only_dirty);
  if (!args->GetNext(&callback)) {
    args->ThrowError();
    return;
  }
  const auto view = web_contents()->GetRenderWidgetHostView();
  if (view) {
    std::unique_ptr<FrameSubscriber> frame_subscriber(new FrameSubscriber(
        isolate(), view, callback, only_dirty));
    view->BeginFrameSubscription(std::move(frame_subscriber));
  }
}
void WebContents::EndFrameSubscription() {