- Electron version: 1.3.6
- Operating system: Windows 7 x64
- Other: Microsoft Office 2013 (will make more sense in a bit)

`shell.openItem()` is a blocking call, it would be nice if it's async or has an async version to handle synchronous external application behavior.

Reproduce: 
Open a password-protected Microsoft Excel file, `shell.openItem()` will be blocking until the Password window is submitted or dismissed. Consequently Microsoft Word does not have this issue.

Related to #2761.

shell/common/api/atom_api_shell.cc
#include <string>
#include "shell/common/gin_converters/callback_converter.h"
#include "shell/common/gin_converters/file_path_converter.h"
#include "shell/common/gin_converters/gurl_converter.h"
#include "shell/common/gin_helper/dictionary.h"
#include "shell/common/gin_helper/error_thrower.h"
#include "shell/common/gin_helper/promise.h"
#include "shell/common/node_includes.h"
#include "shell/common/platform_util.h"
#if defined(OS_WIN)
#include "base/win/scoped_com_initializer.h"
#include "base/win/shortcut.h"
namespace gin {
template <>
struct Converter<base::win::ShortcutOperation> {
  static bool FromV8(v8::Isolate* isolate,