* 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) {
      content::FileChooserFileInfo info;
      info.file_path = path;
      info.display_name = path.BaseName().value();
      file_info.push_back(info);
    }
    OnFilesSelected(file_info);
  }
  void OnFilesSelected(
      const std::vector<content::FileChooserFileInfo>& file_info) {
    if (render_frame_host_)
      render_frame_host_->FilesSelectedInChooser(file_info, mode_);
  }
  
  void RenderFrameHostChanged(content::RenderFrameHost* old_host,
                              content::RenderFrameHost* new_host) override {
    if (old_host == render_frame_host_)
      render_frame_host_ = nullptr;
  }
  
  void RenderFrameDeleted(content::RenderFrameHost* deleted_host) override {
    if (deleted_host == render_frame_host_)
      render_frame_host_ = nullptr;
  }
  
  void WebContentsDestroyed() override { render_frame_host_ = nullptr; }