flex-basis should be 0% (not 0px) when omitted from flex shorthand
rdar://problem/30796872
Created attachment 303242 [details] Patch
Fixed in r213305.
This change caused fast/css/flex-calculated-value.html to fail. I assume this test should have been updated too? https://build.webkit.org/results/Apple%20El%20Capitan%20Release%20WK1%20(Tests)/r213308%20(14227)/results.html
I updated the test in http://trac.webkit.org/projects/webkit/changeset/213315. EWS would have caught this had it been allowed to finish.