- 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/browser/ui/inspectable_web_contents_impl.cc
if (GetDevToolsWebContents()) {
    frontend_loaded_ = false;
    if (managed_devtools_web_contents_) {
      view_->CloseDevTools();
      managed_devtools_web_contents_.reset();
    }
    embedder_message_dispatcher_.reset();
    if (!IsGuest())
      web_contents_->Focus();
  }
}
bool InspectableWebContentsImpl::IsDevToolsViewShowing() {