- 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_linux.cc
#include "shell/common/platform_util.h"
#include <stdio.h>
#include "base/cancelable_callback.h"
#include "base/environment.h"
#include "base/files/file_util.h"
#include "base/nix/xdg_util.h"
#include "base/process/kill.h"
#include "base/process/launch.h"
#include "chrome/browser/ui/libgtkui/gtk_util.h"
#include "url/gurl.h"
#define ELECTRON_TRASH "ELECTRON_TRASH"
namespace {
bool XDGUtil(const std::vector<std::string>& argv, const bool wait_for_exit) {