Merge the Sky Engine changes from the SkyDart branch

sky/tests/layout/document-elementFromPoint.sky

 <sky>
-<import src="../resources/chai.sky" />
-<import src="../resources/mocha.sky" />
 <style>
 foo { width: 100px; height: 100px; background: blue; }
 bar { width: 100px; height: 100px; background: purple; }
 </style>
 <foo /><bar />
 <script>
-describe("elementFromPoint", function() {
-  it("should hit test", function() {
+import "../resources/third_party/unittest/unittest.dart";
+import "../resources/unit.dart";
+
+import "dart:sky";
+
+void main() {
+  initUnit();
+
+  test("should hit test", () {
     // FIXME: We should have much better hit-testing coverage, at least:
     // inline content (both sections of a wrapped run)
     // text node
     // flex box
     // display: paragraph
     // position: absolute
     // position: relative
     // z-order (missing, zero, positive and negative)
-    assert.equal(document.elementFromPoint(50, 50).tagName, 'foo')
-    assert.equal(document.elementFromPoint(50, 150).tagName, 'bar')
-    assert.equal(document.elementFromPoint(50, 250).tagName, 'sky')
+    expect(document.elementFromPoint(50, 50).tagName, equals('foo'));
+    expect(document.elementFromPoint(50, 150).tagName, equals('bar'));
+    expect(document.elementFromPoint(50, 250).tagName, equals('sky'));
   });
-});
+}
 </script>
 </sky>