Merge third_party/brotli/src from https://chromium.googlesource.com/external/font-compression-reference.git at 6cef49677dc4c650ef6e3f56041e0a41803afa8c

This commit was generated by merge_from_chromium.py.

Change-Id: I46222b4d98247fd5bdc0597fc2a012777763a3c9