* 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_window.cc
#include "ui/gfx/geometry/rect.h"
#if defined(TOOLKIT_VIEWS)
#include "atom/browser/native_window_views.h"
#endif
#if defined(OS_WIN)
#include "atom/browser/ui/win/taskbar_host.h"
#include "ui/base/win/shell.h"
#endif
#include "atom/common/node_includes.h"
#if defined(OS_WIN)
namespace mate {
template<>
struct Converter<atom::TaskbarHost::ThumbarButton> {
  static bool FromV8(v8::Isolate* isolate, v8::Handle<v8::Value> val,
                     atom::TaskbarHost::ThumbarButton* out) {
    mate::Dictionary dict;
    if (!ConvertFromV8(isolate, val, &dict))
      return false;
    dict.Get("click", &(out->clicked_callback));
    dict.Get("tooltip", &(out->tooltip));
    dict.Get("flags", &out->flags);
    return dict.Get("icon", &(out->icon));
  }
};
}  
#endif
namespace atom {
namespace api {
namespace {
v8::Local<v8::Value> ToBuffer(v8::Isolate* isolate, void* val, int size) {