* 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
void WebDialogHelper::RunFileChooser(
    content::RenderFrameHost* render_frame_host,
    const content::FileChooserParams& params) {
  std::vector<content::FileChooserFileInfo> result;
  file_dialog::DialogSettings settings;
  settings.force_detached = offscreen_;
  settings.filters = GetFileTypesFromAcceptType(params.accept_types);
  settings.parent_window = window_;
  settings.title = base::UTF16ToUTF8(params.title);
  scoped_refptr<FileSelectHelper> file_select_helper(
      new FileSelectHelper(render_frame_host, params.mode));
  if (params.mode == content::FileChooserParams::Save) {
    settings.default_path = params.default_file_name;
    file_select_helper->ShowSaveDialog(settings);
  } else {
    int flags = file_dialog::FILE_DIALOG_CREATE_DIRECTORY;
    switch (params.mode) {
      case content::FileChooserParams::OpenMultiple:
        flags |= file_dialog::FILE_DIALOG_MULTI_SELECTIONS;
      case content::FileChooserParams::Open:
        flags |= file_dialog::FILE_DIALOG_OPEN_FILE;
        break;