Inline HarfBuzzShaper support functions

Inline a couple of HarfBuzzShaper support functions dealing with
character codes.

R=dglazkov@chromium.org

Review URL: https://codereview.chromium.org/502553002

git-svn-id: svn://svn.chromium.org/blink/trunk@180792 bbb929c8-8fbe-4397-9dbb-9b2b20218538