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/api/atom_api_window.cc
#include "native_mate/constructor.h"
#include "native_mate/dictionary.h"
#include "ui/gfx/geometry/rect.h"
#if defined(TOOLKIT_VIEWS)
#include "atom/browser/native_window_views.h"
#endif
#if defined(OS_WIN)
#include "atom/browser/ui/win/taskbar_host.h"
#endif
#if defined(OS_WIN)
namespace mate {
template<>
struct Converter<atom::TaskbarHost::ThumbarButton> {
  static bool FromV8(v8::Isolate* isolate, v8::Handle<v8::Value> val,
                     atom::TaskbarHost::ThumbarButton* out) {
    mate::Dictionary dict;
    if (!ConvertFromV8(isolate, val, &dict))
      return false;
    dict.Get("click", &(out->clicked_callback));
    dict.Get("tooltip", &(out->tooltip));
    dict.Get("flags", &out->flags);
    return dict.Get("icon", &(out->icon));
  }
};
}  
#endif
namespace atom {
namespace api {
namespace {
v8::Local<v8::Value> ToBuffer(v8::Isolate* isolate, void* val, int size) {