Fix parseAssignableSelector() tests and parse '?.' 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 220 matching lines @@
     Expression expression = pop();
     CascadeExpression receiver = pop();
     pop(); // Token.
     receiver.cascadeSections.add(expression);
     push(receiver);
   }
 
   void handleBinaryExpression(Token token) {
     debugEvent("BinaryExpression");
     if (identical(".", token.stringValue) ||
+        identical("?.", token.stringValue) ||
         identical("..", token.stringValue)) {
       doDotExpression(token);
     } else {
       Expression right = pop();
       Expression left = pop();
       push(ast.binaryExpression(left, toAnalyzerToken(token), right));
     }
   }
 
   void doDotExpression(Token token) {
@@ skipping 916 matching lines @@
       } else {
         // TODO(scheglov): Report error.
         internalError("Invalid modifier ($value). Report an error.");
       }
     }
 
     List<Annotation> metadata = pop();
     // TODO(paulberry): capture doc comments.  See dartbug.com/28851.
     Comment comment = null;
     Token period;
-    void unnamedConstructor(SimpleIdentifier returnType, SimpleIdentifier name) {
+    void unnamedConstructor(
+        SimpleIdentifier returnType, SimpleIdentifier name) {
       push(ast.constructorDeclaration(
           comment,
           metadata,
           toAnalyzerToken(externalKeyword),
           toAnalyzerToken(constKeyword),
           toAnalyzerToken(factoryKeyword),
           returnType,
           toAnalyzerToken(period),
           name,
           parameters,
@@ skipping 209 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);
 }