dart:html perf optimization based on runing Dromaeo benchmarks

samples/third_party/dromaeo/tests/dom-traverse-htmlfast.dart

+#library("dom_traverse");
+#import("dart:html");
+#import('../common/common.dart');
+#import('runner.dart');
+
+
+void main() {
+  final int num = 40;
+
+  // Try to force real results.
+  var ret;
+
+  String html = document.body.innerHTML;
+
+  new Suite(window, 'dom-traverse')
+    .prep(() {
+      html = BenchUtil.replaceAll(html, 'id="test(\\w).*?"', (Match match) {
+        final group = match.group(1);
+        return 'id="test${group}${num}"';
+      });
+      html = BenchUtil.replaceAll(html, 'name="test.*?"', (Match match) {
+        return 'name="test${num}"';
+      });
+      html = BenchUtil.replaceAll(html, 'class="foo.*?"', (Match match) {
+        return 'class="foo test${num} bar"';
+      });
+
+      final div = new Element.tag('div');
+      div.innerHTML = html;
+      document.body.appendChild(div);
+    })
+    .test('firstChild', () {
+      final nodes = document.body.nodes;
+      final nl = nodes.length;
+
+      for (int i = 0; i < num; i++) {
+        for (int j = 0; j < nl; j++) {
+          Node cur = nodes[j];
+          while (cur !== null) {
+            cur = cur.$dom_firstChild;
+          }
+          ret = cur;
+        }
+      }
+    })
+    .test('lastChild', () {
+      final nodes = document.body.nodes;
+      final nl = nodes.length;
+
+      for (int i = 0; i < num; i++) {
+        for (int j = 0; j < nl; j++) {
+          Node cur = nodes[j];
+          while (cur !== null) {
+            cur = cur.$dom_lastChild;
+          }
+          ret = cur;
+        }
+      }
+    })
+    .test('nextSibling', () {
+      for (int i = 0; i < num * 2; i++) {
+        Node cur = document.body.$dom_firstChild;
+        while (cur !== null) {
+          cur = cur.nextNode;
+        }
+        ret = cur;
+      }
+    })
+    .test('previousSibling', () {
+      for (int i = 0; i < num * 2; i++) {
+        Node cur = document.body.$dom_lastChild;
+        while (cur !== null) {
+          cur = cur.previousNode;
+        }
+        ret = cur;
+      }
+    })
+    .test('childNodes', () {
+      for (int i = 0; i < num; i++) {
+        final nodes = document.body.nodes;
+        for (int j = 0; j < nodes.length; j++) {
+          ret = nodes[j];
+        }
+      }
+    })
+    .end();
+}