Revert "Use an explicit 'this' parameter instead of 'This' nodes."

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 303 matching lines @@
   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(${formatReference(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}";
   }
 
   visitGetMutableVariable(cps_ir.GetMutableVariable node) {
     String variable = names.name(node.variable.definition);
@@ skipping 204 matching lines @@
 
   visitLiteralList(cps_ir.LiteralList node) {
     unexpectedNode(node);
   }
   visitLiteralMap(cps_ir.LiteralMap node) {
     unexpectedNode(node);
   }
   visitConstant(cps_ir.Constant node) {
     unexpectedNode(node);
   }
+  visitThis(cps_ir.This node) {
+    unexpectedNode(node);
+  }
   visitReifyTypeVar(cps_ir.ReifyTypeVar node) {
     unexpectedNode(node);
   }
   visitCreateFunction(cps_ir.CreateFunction node) {
     unexpectedNode(node);
   }
   visitGetMutableVariable(cps_ir.GetMutableVariable node) {
     unexpectedNode(node);
   }
   visitParameter(cps_ir.Parameter node) {
@@ skipping 24 matching lines @@
   @override
   visitReadTypeVariable(cps_ir.ReadTypeVariable node) {
     unexpectedNode(node);
   }
 
   @override
   visitReifyRuntimeType(cps_ir.ReifyRuntimeType node) {
     unexpectedNode(node);
   }
 }