Support JS$ prefix for dart and fix bug where _operator_getter and the [] operator were used incons…

tools/dom/scripts/systemhtml.py

Index: tools/dom/scripts/systemhtml.py
diff --git a/tools/dom/scripts/systemhtml.py b/tools/dom/scripts/systemhtml.py
index 24ecbb83e2d036e760a64eac114d1cc7ef442691..09c242d86f8c9bf06e9543800837334734acc123 100644
--- a/tools/dom/scripts/systemhtml.py
+++ b/tools/dom/scripts/systemhtml.py
@@ -614,9 +614,7 @@ class HtmlDartInterfaceGenerator(object):
     return new {0}._internalWrap();
   }}
 
-  factory {0}._internalWrap() {{
-    return new {0}.internal_();
-  }}
+  external factory {0}._internalWrap();
 
   @Deprecated("Internal Use Only")
   {0}.internal_() : super.internal_();