Import css-transitions from wpt.

No-Try: true

Change-Id: Ic5f388ab46010599e7240edf5d1cc5f4694f41ea
Reviewed-on: https://chromium-review.googlesource.com/975042
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545022}

third_party/WebKit/LayoutTests/W3CImportExpectations

@@ -92,7 +92,6 @@ external/wpt/css/css-regions [ Skip ]
 external/wpt/css/css-round-display [ Skip ]
 external/wpt/css/css-ruby [ Skip ]
 external/wpt/css/css-speech [ Skip ]
-external/wpt/css/css-transitions [ Skip ]
 external/wpt/css/filter-effects [ Skip ]
 external/wpt/css/tools [ Skip ]
 external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/README [ Skip ]