* Output of `node_modules/.bin/electron --version`: 4.0.0-beta.8
* Operating System (Platform and Version): Windows 10 1803
* Output of `node_modules/.bin/electron --version` on last known working Electron version (if applicable): 4.0.0-beta.7

**Expected Behavior**
`BrowserWindow.getNativeWindowHandle()` should return different value for different window

**Actual behavior**
`BrowserWindow.getNativeWindowHandle()` returns same value for different window, which is not true nativeWindowHandle for any of them.

**To Reproduce**
Open two `BrowserWindow`, and run `getNativeWindowHandle` on both `BrowserWindow`
```js
const { remote } = require('electron')
w1 = new remote.BrowserWindow()
w2 = new remote.BrowserWindow()
console.log(w1.getNativeWindowHandle(), w2.getNativeWindowHandle())
```
![image](https://user-images.githubusercontent.com/8194131/49328509-7411a800-f5b5-11e8-9a24-827aa589d937.png)


atom/browser/native_window_views.cc
options.Get(options::kMaximizable, &maximizable_);
  
  options.Get("thickFrame", &thick_frame_);
  if (transparent())
    thick_frame_ = false;
#endif
  if (enable_larger_than_screen())
    
    
    
    
    SetContentSizeConstraints(extensions::SizeConstraints(
        gfx::Size(), gfx::Size(INT_MAX / 10, INT_MAX / 10)));
  int width = 800, height = 600;
  options.Get(options::kWidth, &width);
  options.Get(options::kHeight, &height);
  gfx::Rect bounds(0, 0, width, height);
  widget_size_ = bounds.size();
  widget()->AddObserver(this);
  views::Widget::InitParams params;
  params.ownership = views::Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET;
  params.bounds = bounds;
  params.delegate = this;
  params.type = views::Widget::InitParams::TYPE_WINDOW;
  params.remove_standard_frame = !has_frame();
  if (transparent())
    params.opacity = views::Widget::InitParams::TRANSLUCENT_WINDOW;
  
  
  if (transparent() && !has_frame())