Add handling of the HTTP Date header

runtime/bin/http.dart

Index: runtime/bin/http.dart
diff --git a/runtime/bin/http.dart b/runtime/bin/http.dart
index 41a0ac8bdc6a9380e99d717e97b5b89c713f7a9b..b44f380470b5abf0d8a284845ffa92353257437e 100644
--- a/runtime/bin/http.dart
+++ b/runtime/bin/http.dart
@@ -277,6 +277,12 @@ interface HttpHeaders default _HttpHeaders {
   void removeAll(String name);
 
   /**
+   * Gets and sets the date. The value of this property will
+   * reflect the "Date" header
+   */
+  Date date;
+
+  /**
    * Gets and sets the expiry date. The value of this property will
    * reflect the "Expires" header
    */