Harfbuzz requires a set of Unicode-property callbacks, which are currently implemented using data tables in gfxUnicodeProperties. Once we have ICU available, we can use that instead to simplify the implementation and maintenance of this stuff.
Right. And HarfBuzz itself has the glue code to use ICU too.
The glue code to use ICU in harfbuzz is currently used by Android. Chrome has its own based on glib, but Chrome had better use ICU-based one, instead.
Sorry for bug spam. Oops. Chrome has its own table-based code (similar to Mozilla's).