Make arguments of MutationObserver named.

tests/html/mutationobserver_test.dart

Index: tests/html/mutationobserver_test.dart
diff --git a/tests/html/mutationobserver_test.dart b/tests/html/mutationobserver_test.dart
index b2b0ec410d29075c3a3c376a6fd29d77e902869e..3585b85d3dc1800f2d31fa9e3afa64d13c37b0f9 100644
--- a/tests/html/mutationobserver_test.dart
+++ b/tests/html/mutationobserver_test.dart
@@ -49,7 +49,7 @@ main() {
         var div2 = new DivElement();
         var mutationObserver = new MutationObserver(
             mutationCallback(2, orderedEquals([div1, div2])));
-        mutationObserver.observe(container, {'childList': true});
+        mutationObserver.observe(container, options: {'childList': true});
 
         container.nodes.add(div1);
         container.nodes.add(div2);
@@ -61,8 +61,7 @@ main() {
         var div2 = new DivElement();
         var mutationObserver = new MutationObserver(
             mutationCallback(2, orderedEquals([div1, div2])));
-        // OPTIONALS mutationObserver.observe(container, childList: true);
-        mutationObserver.observe(container, {}, true);
+        mutationObserver.observe(container, childList: true);
 
         container.nodes.add(div1);
         container.nodes.add(div2);
@@ -74,8 +73,7 @@ main() {
         var div2 = new DivElement();
         var mutationObserver =
             new MutationObserver(mutationCallback(1, orderedEquals([div1])));
-        // OPTIONALS mutationObserver.observe(container, childList: true);
-        mutationObserver.observe(container, {}, true);
+        mutationObserver.observe(container, childList: true);
 
         container.nodes.add(div1);
         div1.nodes.add(div2);
@@ -89,7 +87,7 @@ main() {
         var mutationObserver = new MutationObserver(
             mutationCallback(2, orderedEquals([div1, div2])));
         mutationObserver.observe(container,
-                                 {'childList': true, 'subtree': true});
+                                 options: {'childList': true, 'subtree': true});
 
         container.nodes.add(div1);
         div1.nodes.add(div2);
@@ -101,8 +99,7 @@ main() {
         var div2 = new DivElement();
         var mutationObserver = new MutationObserver(
             mutationCallback(2, orderedEquals([div1, div2])));
-        // OPTIONALS mutationObserver.observe(container, childList: true, subtree: true);
-        mutationObserver.observe(container, {}, true, null, null, true);
+        mutationObserver.observe(container, childList: true, subtree: true);
 
         container.nodes.add(div1);
         div1.nodes.add(div2);