Work-around for issue 29309

pkg/compiler/lib/src/inferrer/builder.dart

Index: pkg/compiler/lib/src/inferrer/builder.dart
diff --git a/pkg/compiler/lib/src/inferrer/builder.dart b/pkg/compiler/lib/src/inferrer/builder.dart
index 519524c81e29f663ea84a0452cde8d48b18ece35..886d974d3e947569bbb96fc75114c2d625d3f03f 100644
--- a/pkg/compiler/lib/src/inferrer/builder.dart
+++ b/pkg/compiler/lib/src/inferrer/builder.dart
@@ -698,7 +698,11 @@ class ElementGraphBuilder extends ast.Visitor<TypeInformation>
       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);
     });
   }