* Electron Version: Electron 2.0.0
* Operating System: Windows 10

**Expected Behavior**
When a single file extension is given (`<input type="file" accept=".txt" />`), the format description in the open file dialog should not be empty.

**Actual behavior**
When a single file extension is given (`<input type="file" accept=".txt" />`), the format description in the open file dialog is empty.

**To Reproduce**
- open the devtools console in the Electron default app
- run `document.body.innerHTML = '<input type="file" accept=".txt" />';`
- click the "Choose File" button
- observe the file format selection combo box in the bottom-right corner

**Screenshots**
```
<input type="file" accept=".txt" />
```
![one-file](https://user-images.githubusercontent.com/1281234/40083145-8b2c0d92-5893-11e8-9203-f9631dd440ac.PNG)

```
<input type="file" accept=".txt,.zip" />
```
![two-files](https://user-images.githubusercontent.com/1281234/40083146-8b48bece-5893-11e8-9213-980fceee41f1.PNG)

atom/browser/web_dialog_helper.cc
#endif
  {
    std::vector<content::FileChooserFileInfo> file_info;
    if (result) {
      for (auto& path : paths) {
        content::FileChooserFileInfo info;
        info.file_path = path;
        info.display_name = path.BaseName().value();
        file_info.push_back(info);
      }
      if (render_frame_host_ && !paths.empty()) {
        auto* browser_context = static_cast<atom::AtomBrowserContext*>(
            render_frame_host_->GetProcess()->GetBrowserContext());
        browser_context->prefs()->SetFilePath(prefs::kSelectFileLastDirectory,
                                              paths[0].DirName());
      }
    }
    OnFilesSelected(file_info);
  }
#if defined(MAS_BUILD)
  void OnSaveDialogDone(bool result,
                        const base::FilePath& path,
                        const std::string& bookmark)
#else
  void OnSaveDialogDone(bool result, const base::FilePath& path)