Add CPS IR transformation to make the JavaScript backend specific semantics explicit in the tree.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
index c4621cb605b85f18245a5e028eacd95ae3172c4e..b48b6fcea18214a727359efa7c8cd949d5ce47b0 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
@@ -195,4 +195,10 @@ class SExpressionStringifier extends Visitor<String> with Indentation {
     String value = names[node.value.definition];
     return '(IsTrue $value)';
   }
+
+  String visitIdentical(Identical node) {
+    String left = names[node.left.definition];
+    String right = names[node.right.definition];
+    return '(Identical $left $right)';
+  }
 }