dart2js cps: Make Identical a built-in and add Interceptor to Tree IR.

pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
index 47fedb7793795eb69812f94102a19b4c142375dc..ab4b5b0012eb0e6fa00e31c37e26d675c3b86303 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
@@ -515,6 +515,11 @@ class SubexpressionVisitor extends ExpressionVisitor<String> {
   }
 
   @override
+  String visitInterceptor(Interceptor node) {
+    return 'Interceptor(${visitExpression(node.input)})';
+  }
+
+  @override
   String visitForeignExpression(ForeignExpression node) {
     String arguments = node.arguments.map(visitExpression).join(', ');
     return 'Foreign "${node.codeTemplate}"($arguments)';