Short circuit for 'as dynamic'

tool/input_sdk/private/ddc_runtime/operations.dart

Index: tool/input_sdk/private/ddc_runtime/operations.dart
diff --git a/tool/input_sdk/private/ddc_runtime/operations.dart b/tool/input_sdk/private/ddc_runtime/operations.dart
index 9f14816f5d2d1966a8eeec78930087a2a290b1ca..92f62e2ba2a968c8ec46fb76989d01db13f42f22 100644
--- a/tool/input_sdk/private/ddc_runtime/operations.dart
+++ b/tool/input_sdk/private/ddc_runtime/operations.dart
@@ -253,8 +253,7 @@ instanceOf(obj, type) => JS('', '''(() => {
 
 @JSExportName('as')
 cast(obj, type) {
-  if (obj == null) return obj;
-
+  if (JS('bool', '# == #', type, dynamic) || obj == null) return obj;

[Jennifer Messerly, 2016/05/26 18:14:51]

super trivial but: wouldn't null be more common than casts against `dynamic`?

[Leaf, 2016/05/26 18:16:37]

Maybe, but I doubt it.  By far the majority of the casts that I've measured are
against dynamic, because of our generic argument checks (e.g.
List<dynamic>.add(x) casts x to dynamic).

   bool result = strongInstanceOf(obj, type, true);
   if (JS('bool', '#', result)) return obj;
   _throwCastError(obj, type, result);