Fix the length of this expression nodes (issue 5185)

compiler/java/com/google/dart/compiler/parser/DartParser.java

 // Copyright (c) 2012, 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.
 
 package com.google.dart.compiler.parser;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.io.CharStreams;
 import com.google.dart.compiler.DartCompilationError;
@@ skipping 2202 matching lines @@
    *     | identifier
    *     ;
    *
    * fieldFormalParameter
    *    : finalVarOrType? THIS '.' identifier
    *    ;
    * </pre>
    */
   private DartExpression parseParameterName() {
     beginParameterName();
-    if (optional(Token.THIS)) {
+    if (match(Token.THIS)) {
       beginThisExpression();
+      expect(Token.THIS);
+      DartThisExpression thisExpression = done(DartThisExpression.get());
       expect(Token.PERIOD);
-      return done(new DartPropertyAccess(done(DartThisExpression.get()), parseIdentifier()));
+      return done(new DartPropertyAccess(thisExpression, parseIdentifier()));
     }
     return done(parseIdentifier());
   }
 
   /**
    * Validates that given {@link DartParameter}s have no default values, or marks existing default
    * values with given {@link ErrorCode}.
    */
   private void validateNoDefaultParameterValues(List<DartParameter> parameters,
       ErrorCode errorCode) {
@@ skipping 3000 matching lines @@
   private void reportError(DartNode node, ErrorCode errorCode, Object... arguments) {
     if (node != null) {
       reportError(new DartCompilationError(node, errorCode, arguments));
     }
   }
 
   private boolean currentlyParsingToplevel() {
     return   !(isParsingInterface || isTopLevelAbstract || isParsingClass);
   }
 }