Harfbuzz

HOW TO UPDATE
* Check out external/harfbuzz to <checkout_dir>
  ex: git clone https://android.googlesource.com/platform/external/harfbuzz_ng
* Locate the commit you'd like to move.
  ex: for 1.7.4: https://github.com/harfbuzz/harfbuzz/commit/007a2a4317227b8fb4c764c590203c85fc3da5fd
* In <checkout_dir>, run git merge <commit_sha>
  i.e. git merge 007a2a4317227b8fb4c764c590203c85fc3da5fd
* Upload the changes.
  ex: git push origin HEAD:refs/for/master
* Gerrit will run the text related tests.