Fix bad type-inferrence for is-checks in logical and/or expressions.

sdk/lib/_internal/compiler/implementation/inferrer/inferrer_visitor.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.
 
 library inferrer_visitor;
 
 import '../dart2jslib.dart' hide Selector, TypedSelector;
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../tree/tree.dart';
@@ skipping 840 matching lines @@
       LocalsHandler<T> saved = locals;
       locals = new LocalsHandler<T>.from(locals, node);
       updateIsChecks(isChecks, usePositive: true);
       visit(node.arguments.head);
       saved.mergeDiamondFlow(locals, null);
       locals = saved;
       return types.boolType;
     } else if ("||" == op.source) {
       conditionIsSimple = false;
       List<Send> tests = <Send>[];
-      handleCondition(node.receiver, tests);
+      bool isSimple = handleCondition(node.receiver, tests);
       LocalsHandler<T> saved = locals;
       locals = new LocalsHandler<T>.from(locals, node);
-      updateIsChecks(tests, usePositive: false);
+      if (isSimple) updateIsChecks(tests, usePositive: false);
       bool oldAccumulateIsChecks = accumulateIsChecks;
       accumulateIsChecks = false;
       isChecks = null;
       visit(node.arguments.head);
       accumulateIsChecks = oldAccumulateIsChecks;
       saved.mergeDiamondFlow(locals, null);
       locals = saved;
       return types.boolType;
     } else if ("!" == op.source) {
       bool oldAccumulateIsChecks = accumulateIsChecks;
@@ skipping 333 matching lines @@
     return type;
   }
 
   T visitCascade(Cascade node) {
     // Ignore the result of the cascade send and return the type of the cascade
     // receiver.
     visit(node.expression);
     return cascadeReceiverStack.removeLast();
   }
 }