* 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
#include "atom/common/color_util.h"
#include "atom/common/mouse_util.h"
#include "atom/common/native_mate_converters/blink_converter.h"
#include "atom/common/native_mate_converters/callback.h"
#include "atom/common/native_mate_converters/content_converter.h"
#include "atom/common/native_mate_converters/file_path_converter.h"
#include "atom/common/native_mate_converters/gfx_converter.h"
#include "atom/common/native_mate_converters/gurl_converter.h"
#include "atom/common/native_mate_converters/image_converter.h"
#include "atom/common/native_mate_converters/net_converter.h"
#include "atom/common/native_mate_converters/string16_converter.h"
#include "atom/common/native_mate_converters/value_converter.h"
#include "atom/common/options_switches.h"
#include "base/message_loop/message_loop.h"
#include "base/process/process_handle.h"
#include "base/strings/utf_string_conversions.h"
#include "base/threading/thread_task_runner_handle.h"
#include "base/values.h"
#include "brightray/browser/inspectable_web_contents.h"
#include "brightray/browser/inspectable_web_contents_view.h"
#include "chrome/browser/printing/print_preview_message_handler.h"
#include "chrome/browser/printing/print_view_manager_basic.h"
#include "chrome/browser/ssl/security_state_tab_helper.h"
#include "content/browser/renderer_host/render_widget_host_impl.h"
#include "content/browser/renderer_host/render_widget_host_view_base.h"
#include "content/browser/web_contents/web_contents_impl.h"
#include "content/common/view_messages.h"
#include "content/public/browser/child_process_security_policy.h"
#include "content/public/browser/favicon_status.h"
#include "content/public/browser/native_web_keyboard_event.h"