Make it easier and more efficient to use trusted HTML text

tests/html/custom/created_callback_test.dart

Index: tests/html/custom/created_callback_test.dart
diff --git a/tests/html/custom/created_callback_test.dart b/tests/html/custom/created_callback_test.dart
index 769b784a4c4c6b0f32a83163296837a91855b82b..4ce85d2c1b92fcd919a8a8aaa0c47240d10325a6 100644
--- a/tests/html/custom/created_callback_test.dart
+++ b/tests/html/custom/created_callback_test.dart
@@ -86,7 +86,7 @@ main() {
 <x-b id="u"></x-b>
 <x-c id="v"></x-c>
 <x-b id="w"></x-b>
-""", treeSanitizer: new NullTreeSanitizer());
+""", treeSanitizer: NodeTreeSanitizer.trusted);
 
     upgradeCustomElements(div);
 
@@ -136,7 +136,7 @@ main() {
     var tag = ErrorConstructorElement.tag;
     expectGlobalError(() {
       dummy.setInnerHtml('<$tag></$tag>',
-          treeSanitizer: new NullTreeSanitizer());
+          treeSanitizer: NodeTreeSanitizer.trusted);
     });
 
     expect(ErrorConstructorElement.callCount, 1);