* Output of `node_modules/.bin/electron --version`: 2.0.0
* Operating System (Platform and Version): Windows 10

**Expected Behavior**
When I disable a window twice via `setEnabled(false)`, I expect the second disable to have no effect.

**Actual behavior**
The second disable is "queued" up, such that I am forced to enable the window twice to get back to normal.

**To Reproduce**
In the electronquickstart repo, in main.js' `createWindow()`, add these lines:

    mainWindow.setEnabled(false);
    mainWindow.setEnabled(false);
    mainWindow.setEnabled(true);

The window will be disabled when launched. 

You see the same issue if you do it in reverse:

    mainWindow.setEnabled(true);
    mainWindow.setEnabled(false); // this doesn't actually disable it, because the window was enabled from the getgo

If this is expected behavior, can the [docs](https://github.com/electron/electron/blob/master/docs/api/browser-window.md#winsetenabledenable) be updated to explain this behavior.
atom/browser/native_window_views.cc
#if defined(OS_WIN)
  HMENU menu = GetSystemMenu(GetAcceleratedWidget(), false);
  MENUITEMINFO info;
  memset(&info, 0, sizeof(info));
  info.cbSize = sizeof(info);
  info.fMask = MIIM_STATE;
  if (!GetMenuItemInfo(menu, SC_CLOSE, false, &info)) {
    return false;
  }
  return !(info.fState & MFS_DISABLED);
#elif defined(USE_X11)
  return true;
#endif
}
void NativeWindowViews::SetAlwaysOnTop(bool top,
                                       const std::string& level,
                                       int relativeLevel,
                                       std::string* error) {
  if (top != widget()->IsAlwaysOnTop())
    NativeWindow::NotifyWindowAlwaysOnTopChanged();
  widget()->SetAlwaysOnTop(top);
}
bool NativeWindowViews::IsAlwaysOnTop() {
  return widget()->IsAlwaysOnTop();
}
void NativeWindowViews::Center() {