rename `as` helper to make tools happy

lib/runtime/dart_runtime.js

Index: lib/runtime/dart_runtime.js
diff --git a/lib/runtime/dart_runtime.js b/lib/runtime/dart_runtime.js
index 58641ea5be693f7d87622a5a3823c8770b3b197a..041ad24ae10ffbf38af038d9acee8ff54145ea8a 100644
--- a/lib/runtime/dart_runtime.js
+++ b/lib/runtime/dart_runtime.js
@@ -93,13 +93,13 @@ var dart;
   }
   dart.dbinary = dbinary;
 
-  function as(obj, type) {
+  function as_(obj, type) {
     // TODO(vsm): Implement.
     // if (obj == null || is(obj, type)) return obj;
     // throw new core.CastError();
     return obj;
   }
-  dart.as = as;
+  dart.as = as_;
 
   function is(obj, type) {
     // TODO(vsm): Implement.