Don't prevent 'isCycleFree' updating for resynthesized constructors.

We update it in ConstantEvaluationEngine which in general case does
not know whether the constructor is resynthesized or not.

R=brianwilkerson@google.com
BUG=

Review URL: https://codereview.chromium.org/2047103002 .

pkg/analyzer/lib/src/dart/element/element.dart

@@ -2071,7 +2071,8 @@ class ConstructorElementImpl extends ExecutableElementImpl
   }
 
   void set isCycleFree(bool isCycleFree) {
-    assert(serializedExecutable == null);
+    // This property is updated in ConstantEvaluationEngine even for
+    // resynthesized constructors, so we don't have the usual assert here.
     _isCycleFree = isCycleFree;
   }
 

pkg/analyzer/pubspec.yaml

@@ -1,5 +1,5 @@
 name: analyzer
-version: 0.27.4-alpha.9
+version: 0.27.4-alpha.10
 author: Dart Team <misc@dartlang.org>
 description: Static analyzer for Dart.
 homepage: https://github.com/dart-lang/sdk/tree/master/pkg/analyzer