* Output of `node_modules/.bin/electron --version`: 3.0.10, 4.0.0-beta.7
* Operating System (Platform and Version): Ubuntu 18.04
* Output of `node_modules/.bin/electron --version` on last known working Electron version (if applicable): N/A

**Expected Behavior**
When picking a file to upload, the file picker should show a preview of the file when applicable

**Actual behavior**
It does not show a preview...

Chrome shows a preview of the image (tested with 70 and 69).
![chrome](https://user-images.githubusercontent.com/103586/48838688-01b4f280-ed81-11e8-8b38-16d7cbab1f22.png)

Electron shows no preview
![electron](https://user-images.githubusercontent.com/103586/48838699-08dc0080-ed81-11e8-8611-6a199fba23f8.png)


**To Reproduce**
Nothing special, click on a file upload form element...
```html
<input type="file" />
```
Example here: https://cgi-lib.berkeley.edu/ex/fup.html
atom/browser/ui/file_dialog_gtk.cc
for (size_t i = 0; i < filters.size(); ++i) {
    const Filter& filter = filters[i];
    GtkFileFilter* gtk_filter = gtk_file_filter_new();
    for (size_t j = 0; j < filter.second.size(); ++j) {
      auto file_extension =
          std::make_unique<std::string>("." + filter.second[j]);
      gtk_file_filter_add_custom(
          gtk_filter, GTK_FILE_FILTER_FILENAME,
          reinterpret_cast<GtkFileFilterFunc>(FileFilterCaseInsensitive),
          file_extension.release(),
          reinterpret_cast<GDestroyNotify>(OnFileFilterDataDestroyed));
    }
    gtk_file_filter_set_name(gtk_filter, filter.first.c_str());
    gtk_file_chooser_add_filter(GTK_FILE_CHOOSER(dialog_), gtk_filter);
  }
}
}  
bool ShowOpenDialog(const DialogSettings& settings,