Tweak toString() for better type inference

tools/dom/templates/html/dart2js/impl_HTMLAreaElement.darttemplate

Index: tools/dom/templates/html/dart2js/impl_HTMLAreaElement.darttemplate
diff --git a/tools/dom/templates/dart2js_impl.darttemplate b/tools/dom/templates/html/dart2js/impl_HTMLAreaElement.darttemplate
similarity index 59%
copy from tools/dom/templates/dart2js_impl.darttemplate
copy to tools/dom/templates/html/dart2js/impl_HTMLAreaElement.darttemplate
index fb30e0b3e6c13f3fc9f4a6fd21f2603787194b28..df3fdd68cf3b2c1718ee226c3a120ae98866d7cd 100644
--- a/tools/dom/templates/dart2js_impl.darttemplate
+++ b/tools/dom/templates/html/dart2js/impl_HTMLAreaElement.darttemplate
@@ -1,4 +1,4 @@
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
@@ -6,4 +6,9 @@ part of $LIBRARYNAME;
 
 @DocsEditable()
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$MIXINS$IMPLEMENTS {
-$!MEMBERS}
+$!MEMBERS
+
+  @DomName('HTMLAreaElement.toString')
+  @DocsEditable()
+  String toString() => JS('String', 'String(#)', this);
+}