code: function loadTextWithMime(url, headers, overrideMimeType) {
    return Resource.fetch({
      url: url,
      headers: headers,
      overrideMimeType: overrideMimeType
    });
  }
docs: The same as terriajs-cesium/Source/Core/loadText, but with the ability to pass overrideMimeType through to loadWithXhr.
  @private