* 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
return opacity_;
}
void NativeWindowViews::SetIgnoreMouseEvents(bool ignore, bool forward) {
#if defined(OS_WIN)
  LONG ex_style = ::GetWindowLong(GetAcceleratedWidget(), GWL_EXSTYLE);
  if (ignore)
    ex_style |= (WS_EX_TRANSPARENT | WS_EX_LAYERED);
  else
    ex_style &= ~(WS_EX_TRANSPARENT | WS_EX_LAYERED);
  if (layered_)
    ex_style |= WS_EX_LAYERED;
  ::SetWindowLong(GetAcceleratedWidget(), GWL_EXSTYLE, ex_style);
  
  if (!ignore) {
    SetForwardMouseMessages(false);
  } else {
    SetForwardMouseMessages(forward);
  }
#elif defined(USE_X11)
  if (ignore) {
    XRectangle r = {0, 0, 1, 1};
    XShapeCombineRectangles(gfx::GetXDisplay(), GetAcceleratedWidget(),
                            ShapeInput, 0, 0, &r, 1, ShapeSet, YXBanded);
  } else {
    XShapeCombineMask(gfx::GetXDisplay(), GetAcceleratedWidget(), ShapeInput, 0,
                      0, x11::None, ShapeSet);
  }
#endif
}
void NativeWindowViews::SetContentProtection(bool enable) {