Make TypeMask an interface and start hiding implementation details of FlatTypeMask.

sdk/lib/_internal/compiler/implementation/js_backend/emitter.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.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 2257 matching lines @@
         // have a user-defined noSuchMethod implementation. If not, we
         // skip the selector altogether.
 
         // TODO(kasperl): This shouldn't depend on the internals of
         // the type mask. Move more of this code to the type mask.
         ClassElement receiverClass = objectClass;
         TypeMask mask = selector.mask;
         if (mask != null) {
           // If the mask is empty it doesn't contain a noSuchMethod
           // handler -- not even if it is nullable.
-          if (mask.isEmpty) continue;
-          receiverClass = mask.base.element;
+          receiverClass = mask.topClass();

[kasperl, 2013/04/30 14:03:24]

Here we shouldn't compute a receiver class but rather operate on the mask. Could
we redo hasMatchingMember in terms of the mask?

[ngeoffray, 2013/05/01 12:56:16]

Done.

+          if (receiverClass == null) continue;
         }
 
         // If the receiver class is guaranteed to have a member that
         // matches what we're looking for, there's no need to
         // introduce a noSuchMethod handler. It will never be called.
         //
         // As an example, consider this class hierarchy:
         //
         //                   A    <-- noSuchMethod
         //                  / \
@@ skipping 784 matching lines @@
 """;
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;