dart2js cps: Translate identity placeholders to refinement nodes.

pkg/compiler/lib/src/js/js.dart

Index: pkg/compiler/lib/src/js/js.dart
diff --git a/pkg/compiler/lib/src/js/js.dart b/pkg/compiler/lib/src/js/js.dart
index 1a08cfbeb0798072ea178fd3993b134183c5c718..81ee017b58c062936ec1b316c49e52f5db9316fa 100644
--- a/pkg/compiler/lib/src/js/js.dart
+++ b/pkg/compiler/lib/src/js/js.dart
@@ -162,4 +162,10 @@ class UnparsedNode extends DeferredString
 
   @override
   String get value => _literal.value;
-}
+}
+
+/// True if the given template consists of just a placeholder. Such templates
+/// are sometimes used to manually promote the type of an expression.
+bool isIdentityTemplate(Template template) {
+  return template.source == '#';

[sra1, 2016/01/11 19:31:20]

It would be better to check the ast for a placeholder, e.g. how it is done in
https://chromiumcodereview.appspot.com/1567103006/

[asgerf, 2016/01/11 20:11:44]

Replaced with an is-check.

+}