Repro:

create view::Label and set text that contains new line character 0xa.
There is noticeable lag on first render attempt.

After investigation I found:

This character is marked as kMissingGlyphId. 

Following fails due this:
https://cs.chromium.org/chromium/src/ui/gfx/render_text_harfbuzz.cc?q=RenderTextHarfBuzz::CompareFamily&sq=package:chromium&l=1418&dr=CSs

As result following is called:
https://cs.chromium.org/chromium/src/ui/gfx/render_text_harfbuzz.cc?q=RenderTextHarfBuzz::CompareFamily&sq=package:chromium&dr=CSs&l=1500

Which is slow on first time.

Related bug:
b/33252040

In this bug, lag is caused during label::SizeToFit() call.