- 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
CloseDevTools();
}
content::ColorChooser* InspectableWebContentsImpl::OpenColorChooser(
    content::WebContents* source,
    SkColor color,
    const std::vector<blink::mojom::ColorSuggestionPtr>& suggestions) {
  auto* delegate = web_contents_->GetDelegate();
  if (delegate)
    return delegate->OpenColorChooser(source, color, suggestions);
  return nullptr;
}
void InspectableWebContentsImpl::RunFileChooser(
    content::RenderFrameHost* render_frame_host,
    std::unique_ptr<content::FileSelectListener> listener,
    const blink::mojom::FileChooserParams& params) {
  auto* delegate = web_contents_->GetDelegate();
  if (delegate)
    delegate->RunFileChooser(render_frame_host, std::move(listener), params);
}
void InspectableWebContentsImpl::EnumerateDirectory(
    content::WebContents* source,
    std::unique_ptr<content::FileSelectListener> listener,
    const base::FilePath& path) {
  auto* delegate = web_contents_->GetDelegate();
  if (delegate)
    delegate->EnumerateDirectory(source, std::move(listener), path);
}
void InspectableWebContentsImpl::OnWebContentsFocused(