Reading the attack it also only seems to work on browsers that are not doing very good GPU rendering. The process they described, a textbox being rendered on the CPU and uploaded to a texture on every update, is terribly inefficient. That's not what, for example, Android's text renderer does (described in detail here: https://medium.com/@romainguy/androids-font-renderer-c368bbd... )

If the renderer uses a glyph atlas, then there won't be any changes in GPU memory used as you type in a text box. There consequently won't be any time used to update glyphs, as they are already in the atlas (ignoring CJK locales for a minute).