dart:html perf optimization based on runing Dromaeo benchmarks

samples/third_party/dromaeo/tests/dom-attr-html.dart

-#library("dom_attr_html");
+#library("dom_attr");
 #import("dart:html");
-#import("dart:json");
-#source("Common.dart");
-#source("RunnerSuite.dart");
+#import('runner.dart');
 
 void main() {
   final int num = 10240;
 
   // Try to force real results.
   var ret;
 
   Element elem = document.query('#test1');
-  Element a = document.queryAll('a')[0];
+  Element a = document.query('a');
 
   new Suite(window, 'dom-attr')
     .test('getAttribute', () {
       for (int i = 0; i < num; i++)
-        ret = elem.attributes['id'];
+        ret = elem.$dom_getAttribute('id');
     })
     .test('element.property', () {
       for (int i = 0; i < num * 2; i++)
         ret = elem.id;
     })
     .test('setAttribute', () {
         for (int i = 0; i < num; i++)
-        a.attributes['id'] = 'foo';
+        a.$dom_setAttribute('id', 'foo');
     })
     .test('element.property = value', () {
       for (int i = 0; i < num; i++)
         a.id = 'foo';
     })
     .end();
 }