I'd like to take this issue.

Sorry, I already started working on this
https://chromium-review.googlesource.com/c/chromium/src/+/1341289

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/60e2c0cc39b289e9a0c23557ca952348c2bc7630

commit 60e2c0cc39b289e9a0c23557ca952348c2bc7630
Author: Eric Willigers <ericwilligers@chromium.org>
Date: Mon Nov 19 13:19:08 2018

CSS: Serialize % before px in calc

https://drafts.csswg.org/css-values/#math-function-serialize-a-summation
Percentage should be serialized before dimensions with units

Also fix typo in WPTs svg/geometry/parsing/*-computed.svg
calc(50% + 60x) becomes calc(50% + 60px)

BUG=904805

Change-Id: I2ecb732564c405f9315a1ef06e5bd0777c407f19
Reviewed-on: https://chromium-review.googlesource.com/c/1341289
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609262}
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