Implement references to "this" in the new IR.

sdk/lib/_internal/compiler/implementation/dart_backend/tree_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 dart_backend.tracer;
 
 import 'dart:async' show EventSink;
 import '../tracer.dart';
 import 'dart_tree.dart';
 
@@ skipping 44 matching lines @@
   }
 
   visitVariable(Variable node) {}
   visitInvokeStatic(InvokeStatic node) {}
   visitInvokeMethod(InvokeMethod node) {}
   visitInvokeConstructor(InvokeConstructor node) {}
   visitConcatenateStrings(ConcatenateStrings node) {}
   visitLiteralList(LiteralList node) {}
   visitLiteralMap(LiteralMap node) {}
   visitConstant(Constant node) {}
+  visitThis(This node) {}
   visitConditional(Conditional node) {}
   visitLogicalOperator(LogicalOperator node) {}
   visitNot(Not node) {}
 
   visitLabeledStatement(LabeledStatement node) {
     Block target = new Block(node.label);
     breakTargets[node.label] = target;
     visitStatement(node.body);
     _addBlock(target);
     visitStatement(node.next);
@@ skipping 257 matching lines @@
       String value = visitExpression(node.values[i]);
       entries.add("$key: $value");
     }
     return "map [${entries.join(', ')}]";
   }
 
   String visitConstant(Constant node) {
     return "${node.value}";
   }
 
+  String visitThis(This node) {
+    return "this";
+  }
+
   bool usesInfixNotation(Expression node) {
     return node is Conditional || node is LogicalOperator;
   }
 
   String visitConditional(Conditional node) {
     String condition = visitExpression(node.condition);
     String thenExpr = visitExpression(node.thenExpression);
     String elseExpr = visitExpression(node.elseExpression);
     return "$condition ? $thenExpr : $elseExpr";
   }
@@ skipping 38 matching lines @@
       String prefix = v.element == null ? 'v' : '${v.element.name}_';
       while (name == null || _usedNames.contains(name)) {
         name = "$prefix${_counter++}";
       }
       _names[v] = name;
       _usedNames.add(name);
     }
     return name;
   }
 }