* 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 GetNativeWindow()->GetHost()->GetAcceleratedWidget();
}
std::tuple<void*, int> NativeWindowViews::GetNativeWindowHandlePointer() const {
  gfx::AcceleratedWidget handle = GetAcceleratedWidget();
  return std::make_tuple(static_cast<void*>(&handle), sizeof(handle));
}
gfx::Rect NativeWindowViews::ContentBoundsToWindowBounds(
    const gfx::Rect& bounds) const {
  if (!has_frame())
    return bounds;
  gfx::Rect window_bounds(bounds);
#if defined(OS_WIN)
  HWND hwnd = GetAcceleratedWidget();
  gfx::Rect dpi_bounds = display::win::ScreenWin::DIPToScreenRect(hwnd, bounds);
  window_bounds = display::win::ScreenWin::ScreenToDIPRect(
      hwnd,
      widget()->non_client_view()->GetWindowBoundsForClientBounds(dpi_bounds));
#endif
  if (root_view_->HasMenu() && root_view_->IsMenuBarVisible()) {
    int menu_bar_height = root_view_->GetMenuBarHeight();
    window_bounds.set_y(window_bounds.y() - menu_bar_height);
    window_bounds.set_height(window_bounds.height() + menu_bar_height);
  }
  return window_bounds;
}
gfx::Rect NativeWindowViews::WindowBoundsToContentBounds(