Implement CHA through type mask and TypedSelector in the simple type inferrer.

sdk/lib/_internal/compiler/implementation/native_handler.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 native;
 
 import 'dart:collection' show Queue;
 import 'dart:uri';
 import 'dart2jslib.dart' hide SourceString;
 import 'dart_types.dart';
@@ skipping 528 matching lines @@
 
     var firstArg = argNodes.head;
     LiteralString specLiteral = firstArg.asLiteralString();
     if (specLiteral != null) {
       String specString = specLiteral.dartString.slowToString();
       // Various things that are not in fact types.
       if (specString == 'void') return NativeBehavior.NONE;
       if (specString == '' || specString == 'var') {
         var behavior = new NativeBehavior();
         behavior.typesReturned.add(compiler.objectClass.computeType(compiler));
+        behavior.typesReturned.add(compiler.nullClass.computeType(compiler));
         return behavior;
       }
       var behavior = new NativeBehavior();
       for (final typeString in specString.split('|')) {
         var type = _parseType(typeString, compiler,
             (name) => resolver.resolveTypeFromString(name),
             jsCall);
         behavior.typesInstantiated.add(type);
         behavior.typesReturned.add(type);
       }
@@ skipping 336 matching lines @@
   } else {
     if (parameters.parameterCount != 0) {
       compiler.cancel(
           'native "..." syntax is restricted to functions with zero parameters',
           node: nativeBody);
     }
     LiteralString jsCode = nativeBody.asLiteralString();
     builder.push(new HForeign.statement(jsCode.dartString, <HInstruction>[]));
   }
 }