The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/206d90547d33d37cc64234ea9c5adb5350620d51

commit 206d90547d33d37cc64234ea9c5adb5350620d51
Author: Chris Nardi <cnardi@chromium.org>
Date: Sat May 12 06:12:36 2018

Add support for 'x' as a unit of resolution

In https://drafts.csswg.org/css-values-4/#resolution, 'x' is defined as
a synonym for dppx. Add support for parsing 'x' as dots per px.

Intent to Implement and Ship:
https://groups.google.com/a/chromium.org/d/topic/blink-dev/FsD97U77tss

Bug: 630597,  807653 
Change-Id: I70c440c89e42cd005a9c58fd89745a5603e0dee6
Reviewed-on: https://chromium-review.googlesource.com/892467
Commit-Queue: Chris Nardi <cnardi@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558119}
[modify] https://crrev.com/206d90547d33d37cc64234ea9c5adb5350620d51/third_party/WebKit/LayoutTests/external/wpt/html/semantics/embedded-content/the-img-element/sizes/parse-a-sizes-attribute-expected.txt
[modify] https://crrev.com/206d90547d33d37cc64234ea9c5adb5350620d51/third_party/WebKit/LayoutTests/external/wpt/html/semantics/embedded-content/the-img-element/sizes/sizes-iframed.sub.html
[modify] https://crrev.com/206d90547d33d37cc64234ea9c5adb5350620d51/third_party/blink/renderer/core/css/css_primitive_value_units.json5
[modify] https://crrev.com/206d90547d33d37cc64234ea9c5adb5350620d51/third_party/blink/renderer/core/css/parser/css_property_parser_helpers.cc