Adding supported checks and flags to FormData

tools/dom/templates/html/impl/impl_XMLHttpRequest.darttemplate

Index: tools/dom/templates/html/impl/impl_XMLHttpRequest.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_XMLHttpRequest.darttemplate b/tools/dom/templates/html/impl/impl_XMLHttpRequest.darttemplate
index 1b7546435efdb78107705744a9a13371b555f06f..cc8eef3ef8b55d6e3a7dc6e1dd0938bb9e343971 100644
--- a/tools/dom/templates/html/impl/impl_XMLHttpRequest.darttemplate
+++ b/tools/dom/templates/html/impl/impl_XMLHttpRequest.darttemplate
@@ -122,5 +122,29 @@ $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
     return completer.future;
   }
 
+  /**
+   * Checks to see if the Progress event is supported on the current platform.
+   */
+  static bool get supportsProgressEvent {
+$if DART2JS
+    var xhr = new HttpRequest();
+    return JS('bool', '"onprogress" in #', xhr);
+$else
+    return true;
+$endif
+  }
+
+  /**
+   * Checks to see if the LoadEnd event is supported on the current platform.
+   */
+  static bool get supportsLoadEndEvent {

[Emily Fortuna, 2013/02/14 23:51:41]

can these be added to the table of js_support_checks instead?

+$if DART2JS
+    var xhr = new HttpRequest();
+    return JS('bool', '"onloadend" in #', xhr);
+$else
+    return true;
+$endif
+  }
+
 $!MEMBERS
 }