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

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
index cf21ad4c14787ec00f6d7a4bc5e77c78d9f75056..e2b906912415c30c9c21fe21d36ce5aee5f73605 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
@@ -229,6 +229,12 @@ class IRTracer extends TracerUtil implements cps_ir.Visitor {
     return "IsTrue(${names.name(node.value.definition)})";
   }
 
+  visitIdentical(cps_ir.Identical node) {
+    String left = formatReference(node.left);
+    String right = formatReference(node.right);
+    return "Identical($left, $right)";
+  }
+
   visitThis(cps_ir.This node) {
     return "This";
   }