dart:html perf optimization based on runing Dromaeo benchmarks

samples/third_party/dromaeo/tests/dom-query.dart

Index: samples/third_party/dromaeo/tests/dom-query.dart
diff --git a/samples/third_party/dromaeo/tests/dom-query.dart b/samples/third_party/dromaeo/tests/dom-query.dart
index a2e4d0ace5bbd4086244b77838fb1b9bc308dbec..e4d87f185215d90ff930a4a892126a4695f38821 100644
--- a/samples/third_party/dromaeo/tests/dom-query.dart
+++ b/samples/third_party/dromaeo/tests/dom-query.dart
@@ -49,32 +49,42 @@ void main() {
     })
     .test('getElementsByTagName(div)', () {
       for (int i = 0; i < num; i++) {
-        var elems = document.getElementsByTagName('div');
-        ret = elems[elems.length-1].nodeType;
+        final elems = document.getElementsByTagName('div');
+        for (int j = 0, len = elems.length; j < len; j++) {
+          ret = elems[j].hidden;
+        }
       }
     })
     .test('getElementsByTagName(p)', () {
       for (int i = 0; i < num; i++) {
         final elems = document.getElementsByTagName('p');
-        ret = elems[elems.length-1].nodeType;
+        for (int j = 0, len = elems.length; j < len; j++) {
+          ret = elems[j].hidden;
+        }
       }
     })
     .test('getElementsByTagName(a)', () {
       for (int i = 0; i < num; i++) {
-        var elems = document.getElementsByTagName('a');
-        ret = elems[elems.length-1].nodeType;
+        final elems = document.getElementsByTagName('a');
+        for (int j = 0, len = elems.length; j < len; j++) {
+          ret = elems[j].hidden;
+        }
       }
     })
     .test('getElementsByTagName(*)', () {
       for (int i = 0; i < num; i++) {
         var elems = document.getElementsByTagName('*');
-        ret = elems[elems.length-1].nodeType;
+        for (int j = 0, len = elems.length; j < len; j++) {
+          ret = elems[j].hidden;
+        }
       }
     })
     .test('getElementsByTagName (not in document)', () {
       for (int i = 0; i < num; i++) {
-        var elems = document.getElementsByTagName('strong');
-        ret = elems.length == 0;
+        final elems = document.getElementsByTagName('strong');
+        for (int j = 0, len = elems.length; j < len; j++) {
+          ret = elems[j].hidden;
+        }
       }
     })
     .test('getElementsByName', () {