Standalone harness that calls hb_subset_or_fail() the same way
SkPDFSubsetFont.cpp does. Apply from chromium/src/, copy
hvar_overflow_poc.cc to third_party/harfbuzz/fuzz/, then:
  autoninja -C out/asan hvar_overflow_poc
  out/asan/hvar_overflow_poc /path/to/poc.ttf 7282

--- a/third_party/harfbuzz/BUILD.gn
+++ b/third_party/harfbuzz/BUILD.gn
@@ -547,3 +547,9 @@
     seed_corpus = "fuzz/seed_corpus"
   }
 }
+
+executable("hvar_overflow_poc") {
+  testonly = true
+  sources = [ "fuzz/hvar_overflow_poc.cc" ]
+  deps = [ "//third_party/harfbuzz" ]
+}