Merge pull request #10393 from timvandermeij/document

Convert `src/core/document.js` to ES6 syntax

src/core/chunked_stream.js

@@ -12,6 +12,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+/* eslint no-var: error */
 
 import {
   arrayByteLength, arraysToBytes, createPromiseCapability, isEmptyObj,