cps-ir: Add support for intercepted calls.

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

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.ir_tracer;
 
 import 'dart:async' show EventSink;
 
 import 'cps_ir_nodes.dart' as cps_ir hide Function;
 import '../tracer.dart';
@@ skipping 231 matching lines @@
   visitIsTrue(cps_ir.IsTrue node) {
     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)";
   }
 
+  visitInterceptor(cps_ir.Interceptor node) {
+    return "Interceptor(${node.input})";
+  }
+
   visitThis(cps_ir.This node) {
     return "This";
   }
 
   visitReifyTypeVar(cps_ir.ReifyTypeVar node) {
     return "ReifyTypeVar ${node.typeVariable.name}";
   }
 
   visitCreateFunction(cps_ir.CreateFunction node) {
     return "CreateFunction ${node.definition.element.name}";
@@ skipping 153 matching lines @@
     }
   }
 
   visitContinuation(cps_ir.Continuation c) {
     var old_node = current_block;
     current_block = getBlock(c);
     visit(c.body);
     current_block = old_node;
   }
 }