- 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
return devtools_bounds_;
}
void InspectableWebContentsImpl::SaveDevToolsBounds(const gfx::Rect& bounds) {
  pref_service_->Set(kDevToolsBoundsPref, RectToDictionary(bounds));
  devtools_bounds_ = bounds;
}
double InspectableWebContentsImpl::GetDevToolsZoomLevel() const {
  return pref_service_->GetDouble(kDevToolsZoomPref);
}
void InspectableWebContentsImpl::UpdateDevToolsZoomLevel(double level) {
  pref_service_->SetDouble(kDevToolsZoomPref, level);
}
void InspectableWebContentsImpl::ActivateWindow() {