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* Electron version: 1.6.1
* Operating system: macOS

### Expected behavior

navigator.geolocation.getCurrentPosition runs in background

### Actual behavior

the entire UI is frozen

### How to reproduce

```js
    navigator.geolocation.getCurrentPosition((pos) => {
      console.log('POS: ' + pos);
    }, (err) => {
      console.log('Geolocation error: ', err);
    }, {enableHighAccuracy: false});
```
atom/browser/common_web_contents_delegate.cc
const base::FilePath& file_system_path) {
  base::FilePath path = file_system_path;
  if (path.empty()) {
    std::vector<base::FilePath> paths;
    file_dialog::DialogSettings settings;
    settings.parent_window = owner_window();
    settings.properties = file_dialog::FILE_DIALOG_OPEN_DIRECTORY;
    if (!file_dialog::ShowOpenDialog(settings, &paths))
      return;
    path = paths[0];
  }
  std::string file_system_id = RegisterFileSystem(GetDevToolsWebContents(),
                                                  path);
  if (IsDevToolsFileSystemAdded(GetDevToolsWebContents(), path.AsUTF8Unsafe()))
    return;
  FileSystem file_system = CreateFileSystemStruct(GetDevToolsWebContents(),
                                                 file_system_id,
                                                 path.AsUTF8Unsafe());
  std::unique_ptr<base::DictionaryValue> file_system_value(
      CreateFileSystemValue(file_system));
  auto pref_service = GetPrefService(GetDevToolsWebContents());
  DictionaryPrefUpdate update(pref_service, prefs::kDevToolsFileSystemPaths);
  update.Get()->SetWithoutPathExpansion(
      path.AsUTF8Unsafe(), base::Value::CreateNullValue());
  web_contents_->CallClientFunction("DevToolsAPI.fileSystemAdded",
                                    file_system_value.get(),
                                    nullptr, nullptr);
}
void CommonWebContentsDelegate::DevToolsRemoveFileSystem(