Revert "Revert "Converting dart:html to use DateTime rather than Date.""

tools/dom/src/dart2js_Conversions.dart

Index: tools/dom/src/dart2js_Conversions.dart
diff --git a/tools/dom/src/dart2js_Conversions.dart b/tools/dom/src/dart2js_Conversions.dart
index 8b75d7176d4aa001c6e558061dc307e6b2a8878f..7e9ee41aaa11b51c96fcb5a961f021fb0fd2db69 100644
--- a/tools/dom/src/dart2js_Conversions.dart
+++ b/tools/dom/src/dart2js_Conversions.dart
@@ -11,6 +11,15 @@
 
 part of html;
 
+DateTime _convertNativeToDart_DateTime(date) {
+  var millisSinceEpoch = JS('int', '#.getTime()', date);
+  return new DateTime.fromMillisecondsSinceEpoch(millisSinceEpoch, isUtc: true);
+}
+
+_convertDartToNative_DateTime(DateTime date) {
+  return JS('', 'new Date(#)', date.millisecondsSinceEpoch);
+}
+
 WindowBase _convertNativeToDart_Window(win) {
   return _DOMWindowCrossFrame._createSafe(win);
 }