Merge third_party/libyuv from https://chromium.googlesource.com/external/libyuv.git at 5a09c3ef2aa3e6b6da4007746fdde04ca56dae7c

This commit was generated by merge_from_chromium.py.

Change-Id: I4e8f5ebb546970fb9d740a014d950f9be50d47a5