- 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
content::NavigationHandle* navigation_handle) {
  if (navigation_handle->IsInMainFrame() ||
      !navigation_handle->GetURL().SchemeIs("chrome-extension") ||
      !navigation_handle->HasCommitted())
    return;
  content::RenderFrameHost* frame = navigation_handle->GetRenderFrameHost();
  auto origin = navigation_handle->GetURL().GetOrigin().spec();
  auto it = extensions_api_.find(origin);
  if (it == extensions_api_.end())
    return;
  
  
  base::ReplaceFirstSubstringAfterOffset(&it->second, 0, "var chrome",
                                         "var chrome = window.chrome ");
  auto script = base::StringPrintf("%s(\"%s\")", it->second.c_str(),
                                   base::GenerateGUID().c_str());
  
  
  frame->ExecuteJavaScriptForTests(base::UTF8ToUTF16(script),
                                   base::NullCallback());
}
void InspectableWebContentsImpl::SendMessageAck(int request_id,
                                                const base::Value* arg) {
  base::Value id_value(request_id);
  CallClientFunction("DevToolsAPI.embedderMessageAck", &id_value, arg, nullptr);
}
}