Merge third_party/brotli/src from https://chromium.googlesource.com/external/font-compression-reference.git at 7f848593bd2ec83f4537b6d494a5bf55b9bd4456

This commit was generated by merge_from_chromium.py.

Change-Id: I0c8c7ed554118b2b598bd011ec6532676f881e20