Use specific messages for const constructor with body.

pkg/compiler/lib/src/resolution/constructors.dart

Index: pkg/compiler/lib/src/resolution/constructors.dart
diff --git a/pkg/compiler/lib/src/resolution/constructors.dart b/pkg/compiler/lib/src/resolution/constructors.dart
index aa7007231dce00116e7afd07f7428284e973d747..664ac0d9b80cfa37e32665b50bfcb6d34524c87a 100644
--- a/pkg/compiler/lib/src/resolution/constructors.dart
+++ b/pkg/compiler/lib/src/resolution/constructors.dart
@@ -406,7 +406,7 @@ class InitializerResolver {
           // Check that there is no body (Language specification 7.5.1).  If the
           // constructor is also const, we already reported an error in
           // [resolveMethodElement].
-          if (functionNode.hasBody() && !constructor.isConst) {
+          if (functionNode.hasBody && !constructor.isConst) {
             reporter.reportErrorMessage(
                 functionNode, MessageKind.REDIRECTING_CONSTRUCTOR_HAS_BODY);
           }