fix #27672, call computeConstantValue for metadata

pkg/dev_compiler/lib/src/compiler/element_helpers.dart

 // Copyright (c) 2016, 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.
 
 /// Helpers for Analyzer's Element model and corelib model.
 
 import 'package:analyzer/dart/ast/ast.dart'
     show
         ConstructorDeclaration,
         Expression,
@@ skipping 33 matching lines @@
 ///    @js.JS('HTMLFontElement')
 ///    @deprecated
 ///    class FontElement { ... }
 ///
 /// We could match `@deprecated` with a test function like:
 ///
 ///    (v) => v.type.name == 'Deprecated' && v.type.element.library.isDartCore
 ///
 DartObject findAnnotation(Element element, bool test(DartObjectImpl value)) {
   for (var metadata in element.metadata) {
-    var value = metadata.constantValue;
+    var value = metadata.computeConstantValue();
     if (value != null && test(value)) return value;
   }
   return null;
 }
 
 /// Searches all supertype, in order of most derived members, to see if any
 /// [match] a condition. If so, returns the first match, otherwise returns null.
 InterfaceType findSupertype(InterfaceType type, bool match(InterfaceType t)) {
   for (var m in type.mixins.reversed) {
     if (match(m)) return m;
@@ skipping 48 matching lines @@
 ///       const MyAnnotation(this.name/*, ... other params ... */);
 ///     }
 ///
 ///     @MyAnnotation('FooBar')
 ///     main() { ... }
 ///
 /// If we match the annotation for the `@MyAnnotation('FooBar')` this will
 /// return the string 'FooBar'.
 String getAnnotationName(Element element, bool match(DartObjectImpl value)) =>
     findAnnotation(element, match)?.getField('name')?.toStringValue();