Account for boolean operators shortcircuiting behavior

tests/compiler/dart2js/cpa_inference_test.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.
 
 import "package:expect/expect.dart";
 import '../../../sdk/lib/_internal/compiler/implementation/scanner/scannerlib.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/source_file.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/types/types.dart';
 
 import "parser_helper.dart";
@@ skipping 869 matching lines @@
   }
   for (String op in ['&&', '||']) {
     AnalysisResult result = analyze(source(op));
     result.checkNodeHasType('a', [result.bool]);
     result.checkNodeHasType('b', [result.bool]);
     result.checkNodeHasType('c', [result.bool]);
     result.checkNodeHasType('d', [result.bool]);
   }
 }
 
+testBooleanOperatorsShortCirtcuit() {
+  String source(op) {
+    return """
+        main() {
+          var x = null;
+          "foo" $op (x = 42);
+          x;
+        }""";
+  }
+  for (String op in ['&&', '||']) {
+    AnalysisResult result = analyze(source(op));
+    result.checkNodeHasType('x', [result.nullType, result.int]);
+  }
+}
+
 testOperators() {
   final String source = r"""
       class A {
         operator <(x) => 42;
         operator <<(x) => "a";
       }
       main() {
         var x = new A() < "foo";
         var y = new A() << "foo";
         x; y;
@@ skipping 646 matching lines @@
   testGetters();
   testSetters();
   testOptionalNamedParameters();
   testOptionalPositionalParameters();
   testListLiterals();
   testMapLiterals();
   testReturn();
   // testNoReturn(); // right now we infer the empty type instead of null
   testArithmeticOperators();
   testBooleanOperators();
+  testBooleanOperatorsShortCirtcuit();
   testOperators();
   testCompoundOperators1();
   testCompoundOperators2();
   testSetIndexOperator();
   testInequality();
   testFieldInitialization1();
   testFieldInitialization2();
   testFieldInitialization3();
   testSendWithWrongArity();
   testBigTypesWidening1();
   testBigTypesWidening2();
   testDynamicIsAbsorbing();
   testLists();
   testListWithCapacity();
   testEmptyList();
   testJsCall();
   testJsCallAugmentsSeenClasses();
   testIsCheck();
   testSeenClasses();
   testIntDoubleNum();
   testConcreteTypeToTypeMask();
   testSelectors();
   testMixins();
   testClosures();
   testNestedFunctions();
 }