Fix receiver refining optimization in the presence of null: any Object method can be called on the …

sdk/lib/_internal/compiler/implementation/universe/function_set.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 universe;
 
 // TODO(kasperl): This actually holds getters and setters just fine
 // too and stricly they aren't functions. Maybe this needs a better
 // name -- something like ElementSet seems a bit too generic.
 class FunctionSet {
@@ skipping 202 matching lines @@
   TypeMask computeMask(Compiler compiler) {
     if (_mask != null) return _mask;
     return _mask = new TypeMask.unionOf(functions
         .expand((element) {
           ClassElement cls = element.getEnclosingClass();
           return compiler.world.isUsedAsMixin(cls)
               ? ([cls]..addAll(compiler.world.mixinUses[cls]))
               : [cls];
         })
         .map((cls) {
+          if (compiler.backend.isNullImplementation(cls)) {
+            return const TypeMask.empty();
+          }
           return compiler.world.hasSubclasses(cls)
               ? new TypeMask.nonNullSubclass(cls.rawType)
               : new TypeMask.nonNullExact(cls.rawType);
         }),
         compiler);
   }
 
   FullFunctionSetQuery(functions) : super(functions);
 }