1. Create a page with an element that has a relative border-width (e.g., border-width: 0.25em), or view the example at http://jsfiddle.net/W2SdF/
2. Zoom the page in and out.
The border should scale with the rest of the content.
The border scales more rapidly than the rest of the content.
This issue doesn't happen with absolute units like px. It also doesn't happen upon changing the user agent stylesheet's base font size (but of course if I change the base font size and then zoom, the problem does appear).
Downstream chromium bug: http://code.google.com/p/chromium/issues/detail?id=167168
Created attachment 182845 [details]
Attachment 182845 [details] did not pass style-queue:
Failed to run "['Tools/Scripts/check-webkit-style', '--diff-files', u'LayoutTests/ChangeLog', u'LayoutTests/fast..." exit_code: 1
LayoutTests/platform/chromium-linux/svg/zoom/page/zoom-replaced-intrinsic-ratio-001-expected.png:0: Have to enable auto props in the subversion config file (/home/alancutter/.subversion/config "enable-auto-props = yes"). Have to set the svn:mime-type in the subversion config file (/home/alancutter/.subversion/config "*.png = svn:mime-type=image/png"). [image/png] 
Total errors found: 1 in 7 files
If any of these errors are false positives, please file a bug against check-webkit-style.
Created attachment 182847 [details]
Comment on attachment 182847 [details]
Clearing flags on attachment: 182847
Committed r139798: <http://trac.webkit.org/changeset/139798>
All reviewed patches have been landed. Closing bug.
FYI I rebaselined Chromium results in r139832.
Rebaselined http/tests/misc/object-embedding-svg-delayed-size-negotiation-2.htm on Win in r139834.
Weirdly Mac bots still had thin borders. They are covered by an ancient failure expectation from bug 62754.
Thanks Dominic, was waiting for the windows bot to run and forgot about it.