- 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
SetZoomLevelForWebContents(GetDevToolsWebContents(), GetDevToolsZoomLevel());
}
void InspectableWebContentsImpl::CloseWindow() {
  GetDevToolsWebContents()->DispatchBeforeUnload(false );
}
void InspectableWebContentsImpl::LoadCompleted() {
  frontend_loaded_ = true;
  if (managed_devtools_web_contents_)
    view_->ShowDevTools(activate_);
  
  if (!can_dock_) {
    SetIsDocked(DispatchCallback(), false);
  } else {
    if (dock_state_.empty()) {
      const base::DictionaryValue* prefs =
          pref_service_->GetDictionary(kDevToolsPreferences);
      std::string current_dock_state;
      prefs->GetString("currentDockState", &current_dock_state);
      base::RemoveChars(current_dock_state, "\"", &dock_state_);
    }
    base::string16 javascript = base::UTF8ToUTF16(
        "Components.dockController.setDockSide(\"" + dock_state_ + "\");");
    GetDevToolsWebContents()->GetMainFrame()->ExecuteJavaScript(
        javascript, base::NullCallback());
  }
  if (view_->GetDelegate())
    view_->GetDelegate()->DevToolsOpened();
}
void InspectableWebContentsImpl::SetInspectedPageBounds(const gfx::Rect& rect) {