It seems that the computed value and CSSOM serialization for several grid shorthands is not right. For detailed list and example to reproduce the issue, check this thread on www-style: https://lists.w3.org/Archives/Public/www-style/2015Jul/0242.html The following W3C test can be used to check the cases that are failing in Chrome: http://test.csswg.org/shepherd/testcase/grid-layout-properties/spec/css-grid-1/
Note that the expected behavior is not 100% confirmed yet: https://github.com/w3c/csswg-drafts/issues/1041