Import display: contents tests from csswg-test.

third_party/WebKit/LayoutTests/imported/csswg-test/css-display-3/display-contents-computed-style.html

Index: third_party/WebKit/LayoutTests/imported/csswg-test/css-display-3/display-contents-computed-style.html
diff --git a/third_party/WebKit/LayoutTests/imported/csswg-test/css-display-3/display-contents-computed-style.html b/third_party/WebKit/LayoutTests/imported/csswg-test/css-display-3/display-contents-computed-style.html
index 8b48c27cb709476ee34c8e1215330acef14dc630..5f232f26105eab596669afa4a6c541d80e58b285 100644
--- a/third_party/WebKit/LayoutTests/imported/csswg-test/css-display-3/display-contents-computed-style.html
+++ b/third_party/WebKit/LayoutTests/imported/csswg-test/css-display-3/display-contents-computed-style.html
@@ -3,11 +3,12 @@
 <title>CSS Display: Computed style for display:contents</title>
 <link rel="author" title="Rune Lillesveen" href="mailto:rune@opera.com">
 <link rel="help" href="https://drafts.csswg.org/css-display-3/#valdef-display-contents">
+<link rel="help" href="https://drafts.csswg.org/css-display-3/#transformations">
 <link rel="help" href="https://drafts.csswg.org/cssom-1/#resolved-values">
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <style>
-    .contents { display: contents }
+    html, .contents { display: contents }
 
     #t2 .contents { background-color: green }
     #t2 span { background-color: inherit }
@@ -66,4 +67,8 @@
         assert_equals(computed.marginLeft, "25%");
         assert_equals(computed.paddingTop, "10%");
     }, "Resolved value should be computed value, not used value, for display:contents");
+
+    test(function(){
+        assert_equals(getComputedStyle(document.documentElement).display, "block");
+    }, "display:contents is blockified for root elements");
 </script>