Make ElementTests independent of the existing HTML markup.

client/tests/client/html/ElementTests.dart

Index: client/tests/client/html/ElementTests.dart
diff --git a/client/tests/client/html/ElementTests.dart b/client/tests/client/html/ElementTests.dart
index 6d0bf35afeb4ca2a245a4e564b53c311c3c88ed4..6e67c3d65c26dc160aff695a54eb907c938df380 100644
--- a/client/tests/client/html/ElementTests.dart
+++ b/client/tests/client/html/ElementTests.dart
@@ -51,7 +51,14 @@ void testElement() {
   });
 
   asyncTest('rect', 1, () {
-    final element = document.body;
+    final container = new Element.tag("div");
+    container.style.position = 'absolute';
+    final element = new Element.tag("div");
+    element.style.width = '200px';
+    element.style.height = '200px';
+    container.elements.add(element);
+    document.body.elements.add(container);
+
     element.rect.then((rect) {
       expectLargeRect(rect.client);
       expectLargeRect(rect.offset);
@@ -59,6 +66,7 @@ void testElement() {
       Expect.equals(rect.bounding.left, 8);
       Expect.equals(rect.bounding.top, 8);
       Expect.isTrue(rect.clientRects.length > 0);
+      container.remove();
       callbackDone();
     });
   });