[css-grid] Import W3C Test Suite

This patch imports the CSS Grid Layout test suite from csswg-test repository.

Currently we're passing most of the but:
* grid-layout-properties.html: An old known bug (crbug.com/511177).
* grid-support-grid-template-areas-001.xht &
  grid-inline-support-grid-template-areas-001.xht: Because of an issue
  with testharness.js (crbug.com/687492).

Additionally I'm skipping the tests related to "Implied Minimum Size
of Grid Items" (https://drafts.csswg.org/css-grid/#min-size-auto),
because the test suite needs to be updated after the CSS WG resolves
the following issue: https://github.com/w3c/csswg-drafts/issues/283
See crbug.com/666940 for more details.

BUG=687494

Review-Url: https://codereview.chromium.org/2670473003
Cr-Commit-Position: refs/heads/master@{#447562}
229 files changed