dart:html perf optimization based on runing Dromaeo benchmarks

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

 #library("dom_query");
 #import("dart:dom");
 #import('../common/common.dart');
 #import('runner.dart');
 
 void main() {
   final int num = 40;
 
   // Try to force real results.
   var ret;
@@ skipping 31 matching lines @@
         ret = document.getElementById('testA');
         ret = document.getElementById('testB');
         ret = document.getElementById('testC');
         ret = document.getElementById('testD');
         ret = document.getElementById('testE');
         ret = document.getElementById('testF');
       }
     })
     .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', () {
       for (int i = 0; i < num * 20; i++) {
         var elems = document.getElementsByName('test$num');
         ret = elems[elems.length-1].nodeType;
         elems = document.getElementsByName('test$num');
         ret = elems[elems.length-1].nodeType;
         elems = document.getElementsByName('test$num');
         ret = elems[elems.length-1].nodeType;
         elems = document.getElementsByName('test$num');
         ret = elems[elems.length-1].nodeType;
       }
     })
     .test('getElementsByName (not in document)', () {
       for (int i = 0; i < num * 20; i++) {
         ret = document.getElementsByName('test').length == 0;
         ret = document.getElementsByName('test').length == 0;
         ret = document.getElementsByName('test').length == 0;
         ret = document.getElementsByName('test').length == 0;
         ret = document.getElementsByName('test').length == 0;
       }
     })
     .end();
 }