More extensive error handling for 'unresolved' cases.

lib/kernel_visitor.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.md file.
 
 library rasta.kernel_visitor;
 
 import 'package:kernel/ast.dart' as ir;
 
-import 'package:kernel/accessors.dart' show
+import 'package:kernel/frontend/accessors.dart' show
     Accessor,
     IndexAccessor,
     NullAwarePropertyAccessor,
     PropertyAccessor,
     ReadOnlyAccessor,
     StaticAccessor,
     SuperIndexAccessor,
     SuperPropertyAccessor,
     ThisPropertyAccessor,
     VariableAccessor,
@@ skipping 3010 matching lines @@
       : this(null, true, node, initializers);
 
   accept(ir.Visitor v) => throw "unsupported";
 
   visitChildren(ir.Visitor v) => throw "unsupported";
 
   String toString() {
     return "IrFunction($kind, $isConstructor, $node, $initializers)";
   }
 }