Auto merge of #13192 - notriddle:master, r=pcwalton

Account for percentages in fixed table layout

Don't just use the minimum length all the time.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #13166 (github issue number if applicable).
- [X] There are tests for these changes

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tests/wpt/metadata-css/css21_dev/html4/floats-149.htm.ini

@@ -1,3 +0,0 @@
-[floats-149.htm]
-  type: reftest
-  expected: FAIL