Parse 'x.y' as PrefixedIdentifier, not PropertyAccess with Fasta.

pkg/front_end/lib/src/fasta/analyzer/ast_builder.dart

 // Copyright (c) 2016, 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 fasta.analyzer.ast_builder;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast_factory.dart' show AstFactory;
 import 'package:analyzer/dart/ast/standard_ast_factory.dart' as standard;
 import 'package:analyzer/dart/ast/token.dart' as analyzer show Token;
@@ skipping 236 matching lines @@
       Expression right = pop();
       Expression left = pop();
       push(ast.binaryExpression(left, toAnalyzerToken(token), right));
     }
   }
 
   void doDotExpression(Token token) {
     Expression identifierOrInvoke = pop();
     Expression receiver = pop();
     if (identifierOrInvoke is SimpleIdentifier) {
-      push(ast.propertyAccess(
-          receiver, toAnalyzerToken(token), identifierOrInvoke));
+      if (receiver is SimpleIdentifier && identical('.', token.stringValue)) {
+        push(ast.prefixedIdentifier(
+            receiver, toAnalyzerToken(token), identifierOrInvoke));
+      } else {
+        push(ast.propertyAccess(
+            receiver, toAnalyzerToken(token), identifierOrInvoke));
+      }
     } else if (identifierOrInvoke is MethodInvocation) {
       assert(identifierOrInvoke.target == null);
       identifierOrInvoke
         ..target = receiver
         ..operator = toAnalyzerToken(token);
       push(identifierOrInvoke);
     } else {
       internalError(
           "Unhandled property access: ${identifierOrInvoke.runtimeType}");
     }
@@ skipping 1132 matching lines @@
 }
 
 /// Data structure placed on the stack to represent the keyword "operator"
 /// followed by a token.
 class _OperatorName {
   final Token operatorKeyword;
   final SimpleIdentifier name;
 
   _OperatorName(this.operatorKeyword, this.name);
 }