Implement references to "this" in the new IR.

sdk/lib/_internal/compiler/implementation/ir/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 'ir_nodes.dart' as ir hide Function;
 import '../tracer.dart';
@@ skipping 144 matching lines @@
     }
     printStmt(dummy, "LiteralMap (${entries.join(', ')})");
   }
 
   visitInvokeConstConstructor(ir.InvokeConstConstructor node) {
     String dummy = names.name(node);
     String values = node.arguments.map(formatReference).join(', ');
     printStmt(dummy, "ConstConstruction ($values)");
   }
 
-
+  visitThis(ir.This node) {
+    String dummy = names.name(node);
+    printStmt(dummy, "This");
+  }
 
   visitInvokeContinuation(ir.InvokeContinuation node) {
     String dummy = names.name(node);
     String kont = formatReference(node.continuation);
     String args = node.arguments.map(formatReference).join(', ');
     printStmt(dummy, "InvokeContinuation $kont ($args)");
   }
 
   visitBranch(ir.Branch node) {
     String dummy = names.name(node);
@@ skipping 165 matching lines @@
     }
   }
 
   visitContinuation(ir.Continuation c) {
     var old_node = current_block;
     current_block = getBlock(c);
     visit(c.body);
     current_block = old_node;
   }
 }