Import display: contents tests from csswg-test.

third_party/WebKit/LayoutTests/imported/csswg-test/css-display-3/support/acid.css

+html, body {
+  color: black;
+  background-color: white;
+  font-size: 16px;
+  padding: 0;
+  margin: 0;
+}
+
+body { color: red; }
+
+.table {
+  display: table;
+  border-collapse: collapse;
+  border: blue solid 1pt;
+}
+
+.itable { display: inline-table; }
+.caption { display: table-caption; }
+.cell {
+  display: table-cell;
+  border: inherit;
+}
+.row {
+  display: table-row;
+  border: green dashed 1pt;
+}
+.rowg { display: table-row-group; }
+.head { display: table-header-group; }
+.foot { display: table-footer-group; }
+.col { display: table-column; }
+.colg { display: table-column-group; }
+.flex { display: flex; }
+.iflex { display: inline-flex; }
+.li { display: list-item; }
+.ib { display: inline-block; }
+.inline { display: inline; }
+.columns { columns: 2; height: 4em; }
+.contents {
+  display: contents;
+  align-items: inherit;
+  justify-items:inherit;
+}
+.c1 { color: lime; }
+.c2 { background: blue; color: pink; }
+.c3 { color: teal; }
+.c4 { color: green; }
+.c5 { color: silver; }
+.c6 { color: cyan; }
+.c7 { color: magenta; }
+.c8 { color: yellow; }
+.c9 { color: grey; }
+.c10{ color: black; }
+.b { background: inherit; }
+
+/** This is the only difference between references and non-reference styles */
+.ref .c2 { background: transparent; }
+.ref .b { background:blue; }
+.ref div.contents { display: block; }
+.ref span.contents { display: inline; }