ComplexTextController doubly applies space characters’ synthetic bold offset. This is because adjustGlyphsAndAdvances() calls fontData->spaceWidth() [which comes from SimpleFontData::platformWidthForGlyph() and thus includes m_syntheticBoldOffset] but then proceeds to unconditionally adds fontData->syntheticBoldOffset().
UniscribeController::shapeAndPlaceItem() does the same thing, so I’ll apply a blind fix to it at the same time.
Created attachment 109092 [details]
I'm not sure why my patch failed the style queue since it succeeds on my machine with r96265.
Comment on attachment 109092 [details]
Attachment 109092 [details] did not pass chromium-ews (chromium-xvfb):
New failing tests:
Landed in <http://trac.webkit.org/r96404>.