Log Message:
harfbuzz: update to 1.7.4.

harfbuzz: update to 1.7.4.

Overview of changes leading to 1.7.4
Wednesday, December 20, 2017
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- Fix collect_glyphs() regression caused by hb_set_t changes.

Overview of changes leading to 1.7.3
Monday, December 18, 2017
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- hb_set_t performance tuning and optimizations.
- Speed up collect_glyphs() and reject garbage data.
- In hb_coretext_font_create() set font point-size (ptem).
- Misc fixes.

Overview of changes leading to 1.7.2
Monday, December 4, 2017
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- Optimize hb_set_add_range().
- Misc fixes.
- New API:
hb_coretext_font_create()