- 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/platform_util.h
#ifndef SHELL_COMMON_PLATFORM_UTIL_H_
#define SHELL_COMMON_PLATFORM_UTIL_H_
#include <string>
#include "base/callback_forward.h"
#include "base/files/file_path.h"
#include "build/build_config.h"
#if defined(OS_WIN)
#include "base/strings/string16.h"
#endif
class GURL;