This test is checking for specific size of the Chinese characters, but our ahem.ttf font doesn't have them (according to fontdrop.info). This causes the browser to fallback to a local font, which can be different from one computer to another.

This causes HHH to fail, for example:

https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket.appspot.com/8846622841805053712/+/u/flutter_test_web_tests/stdout

Somehow the C++ engine is immune to this problem. Perhaps it also falls back to some font, but that fallback font is stable across machines.