Add visitor methods specific to ??= to SemanticSendVisitor.

pkg/compiler/lib/src/use_unused_api.dart

 // 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.
 
 /// This file use methods that aren't used by dart2js.dart, but that we wish to
 /// keep anyway. This might be general API that isn't currently in use,
 /// debugging aids, or API only used for testing (see TODO below).
 
 library dart2js.use_unused_api;
 
@@ skipping 307 matching lines @@
 }
 
 useProgramBuilder(program_builder.ProgramBuilder builder) {
   builder.buildMethodHackForIncrementalCompilation(null);
   builder.buildFieldsHackForIncrementalCompilation(null);
 }
 
 useSemanticVisitor() {
   operators.UnaryOperator.fromKind(null);
   operators.BinaryOperator.fromKind(null);
-  new semantic_visitor.BulkSendVisitor()
-      ..apply(null, null)
-      ..visitSuperFieldFieldCompound(null, null, null, null, null, null);
+  new semantic_visitor.BulkSendVisitor()..apply(null, null);
   new semantic_visitor.TraversalVisitor(null).apply(null, null);
   new semantic_visitor.BulkDeclarationVisitor().apply(null, null);
 }
 
 class TreeVisitor1 extends tree_ir.ExpressionVisitor1
                       with tree_ir.StatementVisitor1 {
   noSuchMethod(inv) {}
 }
 
 useTreeVisitors() {
   new TreeVisitor1().visitExpression(null, null);
   new TreeVisitor1().visitStatement(null, null);
 }