Work-around for issue 29309

pkg/compiler/lib/src/inferrer/builder.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 simple_types_inferrer;
 
 import '../closure.dart' show ClosureClassMap;
 import '../common.dart';
 import '../common/names.dart' show Identifiers, Selectors;
 import '../compiler.dart' show Compiler;
@@ skipping 680 matching lines @@
       updateIsChecks(tests, usePositive: true);
       visit(node.body);
     });
   }
 
   TypeInformation visitDoWhile(ast.DoWhile node) {
     return handleLoop(node, () {
       visit(node.body);
       List<ast.Send> tests = <ast.Send>[];
       handleCondition(node.condition, tests);
-      updateIsChecks(tests, usePositive: true);
+      // TODO(29309): This condition appears to stengthen both the back-edge and
+      // exit-edge. For now, avoid strengthening on the condition until the
+      // proper fix is found.
+      //
+      //     updateIsChecks(tests, usePositive: true);
     });
   }
 
   TypeInformation visitFor(ast.For node) {
     visit(node.initializer);
     return handleLoop(node, () {
       List<ast.Send> tests = <ast.Send>[];
       handleCondition(node.condition, tests);
       updateIsChecks(tests, usePositive: true);
       visit(node.body);
@@ skipping 2228 matching lines @@
     Selector moveNextSelector = Selectors.moveNext;
     TypeMask moveNextMask = inTreeData.typeOfIteratorMoveNext(node);
 
     TypeInformation iteratorType = handleDynamicSend(node, iteratorSelector,
         iteratorMask, expressionType, new ArgumentsTypes.empty());
 
     return handleForInLoop(node, iteratorType, currentSelector, currentMask,
         moveNextSelector, moveNextMask);
   }
 }