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

tests/compiler/dart2js/simple_inferrer_test.dart

 // Copyright (c) 2013, 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.
 
 import 'package:expect/expect.dart';
 import
     '../../../sdk/lib/_internal/compiler/implementation/types/types.dart'
     show TypeMask;
 
 import 'compiler_helper.dart';
@@ skipping 423 matching lines @@
 
 testSpecialization2() {
   var a = topLevelGetter();
   // Make [a] a captured variable. This should disable receiver
   // specialization on [a].
   (() => a.toString())();
   a - 42;
   return a;
 }
 
+testSpecialization3() {
+  var a = returnDynamic() ? null : 42;
+  a.toString();
+  // Test that calling an [Object] method on [a] will not lead to
+  // infer that [a] is not null;
+  return a;
+}
+
 testReturnInvokeDynamicGetter() => new A().myFactory();
 
 var topLevelConstList = const [42];
 
 get topLevelGetter => 42;
 returnDynamic() => topLevelGetter(42);
 returnTopLevelGetter() => topLevelGetter;
 
 class A {
   factory A() = A.generative;
@@ skipping 121 matching lines @@
          ..returnInt8()
          ..returnInt9();
   testReturnElementOfConstList1();
   testReturnElementOfConstList2();
   testReturnItselfOrInt(topLevelGetter());
   testReturnInvokeDynamicGetter();
   testCascade1();
   testCascade2();
   testSpecialization1();
   testSpecialization2();
+  testSpecialization3();
 }
 """;
 
 void main() {
   Uri uri = new Uri(scheme: 'source');
   var compiler = compilerFor(TEST, uri);
   compiler.runCompiler(uri);
   var typesTask = compiler.typesTask;
   var typesInferrer = typesTask.typesInferrer;
 
@@ skipping 104 matching lines @@
     Expect.equals(new TypeMask.nonNullExact(cls.rawType),
                   typesInferrer.getReturnTypeOfElement(element));
   }
   checkFactoryConstructor('A', '');
 
   checkReturn('testCascade1', typesTask.growableListType);
   checkReturn('testCascade2', new TypeMask.nonNullExact(
       typesTask.rawTypeOf(findElement(compiler, 'CascadeHelper'))));
   checkReturn('testSpecialization1', typesTask.numType);
   checkReturn('testSpecialization2', typesTask.dynamicType);
+  checkReturn('testSpecialization3', typesTask.intType.nullable());
 }