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

sdk/lib/_internal/compiler/implementation/universe/universe.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.
 
 library universe;
 
 import '../closure.dart';
 import '../elements/elements.dart';
 import '../dart2jslib.dart';
 import '../dart_types.dart';
@@ skipping 404 matching lines @@
   final Selector asUntyped;
   final TypeMask mask;
 
   TypedSelector(this.mask, Selector selector)
       : asUntyped = selector.asUntyped,
         super(selector.kind,
               selector.name,
               selector.library,
               selector.argumentCount,
               selector.namedArguments) {
-    // Invariant: Typed selector can not be based on a malformed type.
-    assert(mask.isEmpty || !identical(mask.base.kind, TypeKind.MALFORMED_TYPE));
     assert(asUntyped.mask == null);
   }
 
   TypedSelector.exact(DartType base, Selector selector)
       : this(new TypeMask.exact(base), selector);
 
   TypedSelector.subclass(DartType base, Selector selector)
       : this(new TypeMask.subclass(base), selector);
 
   TypedSelector.subtype(DartType base, Selector selector)
       : this(new TypeMask.subtype(base), selector);
 
-  bool get hasExactMask => mask.isExact;
 
   bool appliesUnnamed(Element element, Compiler compiler) {
     assert(sameNameHack(element, compiler));
     // [TypedSelector] are only used after resolution.
     assert(compiler.phase > Compiler.PHASE_RESOLVING);
     if (!element.isMember()) return false;
 
     // A closure can be called through any typed selector:
     // class A {
     //   get foo => () => 42;
     //   bar() => foo(); // The call to 'foo' is a typed selector.
     // }
     if (element.getEnclosingClass().isClosure()) {
       return appliesUntyped(element, compiler);
     }
 
     if (!mask.canHit(element, this, compiler)) return false;
     return appliesUntyped(element, compiler);
   }
 }