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
if (!has_frame())
    return size;
  gfx::Size content_size(size);
#if defined(OS_WIN)
  HWND hwnd = GetAcceleratedWidget();
  content_size = display::win::ScreenWin::DIPToScreenSize(hwnd, content_size);
  RECT rect;
  SetRectEmpty(&rect);
  DWORD style = ::GetWindowLong(hwnd, GWL_STYLE);
  DWORD ex_style = ::GetWindowLong(hwnd, GWL_EXSTYLE);
  AdjustWindowRectEx(&rect, style, FALSE, ex_style);
  content_size.set_width(content_size.width() - (rect.right - rect.left));
  content_size.set_height(content_size.height() - (rect.bottom - rect.top));
  content_size = display::win::ScreenWin::ScreenToDIPSize(hwnd, content_size);
#endif
  if (menu_bar_ && menu_bar_visible_)
    content_size.set_height(content_size.height() - kMenuBarHeight);
  return content_size;
}
void NativeWindowViews::HandleKeyboardEvent(