We can get the content size and the window size, but not the chrome position.

At the moment we do this:

```
leftBorderWidth = (windowWidth - contentWidth) / 2;
titlebarHeight = windowHeight - (contentHeight + leftBorderWidth);
```

which makes some assumptions so therefore feels a bit wrong.

it would be nice if alongside getContentSize (https://github.com/electron/electron/blob/master/docs/api/browser-window.md#wingetcontentsize) there was a getContentOffset.

I've been looking at the C++ - https://github.com/electron/electron/blob/e05804848f98959d63337aacd9047cd579c5b23f/chromium_src/extensions/browser/app_window/size_constraints.cc and I don't see an easy way to get this information - do you have any ideas or pointers if you accept this as a feature request?

atom/browser/native_window_views.cc
brightray::InspectableWebContents* web_contents,
    const mate::Dictionary& options,
    NativeWindow* parent)
    : NativeWindow(web_contents, options, parent),
      window_(new views::Widget),
      web_view_(inspectable_web_contents()->GetView()->GetView()),
      menu_bar_autohide_(false),
      menu_bar_visible_(false),
      menu_bar_alt_pressed_(false),
#if defined(OS_WIN)
      enabled_a11y_support_(false),
      thick_frame_(true),
#endif
      keyboard_event_handler_(new views::UnhandledKeyboardEventHandler),
      disable_count_(0),
      use_content_size_(false),
      movable_(true),
      resizable_(true),
      maximizable_(true),
      minimizable_(true),
      fullscreenable_(true) {
  options.Get(options::kTitle, &title_);
  options.Get(options::kAutoHideMenuBar, &menu_bar_autohide_);
#if defined(OS_WIN)