Use specific messages for const constructor with body.

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.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 dart2js.ir_builder_task;
 
 import '../closure.dart' as closure;
 import '../common.dart';
 import '../common/names.dart' show
     Identifiers,
@@ skipping 290 matching lines @@
     // TODO(asgerf): This is largely inherited from the SSA builder.
     // The ConstructorBodyElement has an invalid function signature, but we
     // cannot add a BoxLocal as parameter, because BoxLocal is not an element.
     // Instead of forging ParameterElements to forge a FunctionSignature, we
     // need a way to create backend methods without creating more fake elements.
     assert(constructor.isGenerativeConstructor);
     assert(constructor.isImplementation);
     if (constructor.isSynthesized) return null;
     ast.FunctionExpression node = constructor.node;
     // If we know the body doesn't have any code, we don't generate it.
-    if (!node.hasBody()) return null;
-    if (node.hasEmptyBody()) return null;
+    if (!node.hasBody) return null;
+    if (node.hasEmptyBody) return null;
     ClassElement classElement = constructor.enclosingClass;
     ConstructorBodyElement bodyElement;
     classElement.forEachBackendMember((Element backendMember) {
       if (backendMember.isGenerativeConstructorBody) {
         ConstructorBodyElement body = backendMember;
         if (body.constructor == constructor) {
           bodyElement = backendMember;
         }
       }
     });
@@ skipping 3720 matching lines @@
     _backend.jsInteropAnalysis.hasAnonymousAnnotation(element.contextClass);
 
   String getJsInteropTargetPath(FunctionElement element) {
     return '${_backend.namer.fixedBackendPath(element)}.'
       '${_backend.getFixedBackendName(element)}';
   }
 
   DartType get jsJavascriptObjectType =>
     _backend.helpers.jsJavaScriptObjectClass.thisType;
 }