[OTS] update woff2 implementation

Manually ported from font-compression-reference repository.

https://code.google.com/p/font-compression-reference/source/detail?r=47c5016d7f20363602601aa2624229482b5c2e50

TEST=compiled
R=ksakamoto@chromium.org

Review URL: https://codereview.chromium.org/261563002