Ensure that a complete library element has constants evaluated (issue 24890)

pkg/analysis_server/lib/src/analysis_server.dart

Index: pkg/analysis_server/lib/src/analysis_server.dart
diff --git a/pkg/analysis_server/lib/src/analysis_server.dart b/pkg/analysis_server/lib/src/analysis_server.dart
index f72f051e2077cad3b693bd2d28a4b37564ffc451..1788aae63db1faa51673c4b15d320dc5d781b40b 100644
--- a/pkg/analysis_server/lib/src/analysis_server.dart
+++ b/pkg/analysis_server/lib/src/analysis_server.dart
@@ -34,6 +34,7 @@ import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:analyzer/src/generated/utilities_general.dart';
+import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/src/util/glob.dart';
 import 'package:plugin/plugin.dart';
 
@@ -1330,7 +1331,7 @@ class AnalysisServer {
     }
     // if library has not been resolved yet, the unit will be resolved later
     Source librarySource = librarySources[0];
-    if (context.getLibraryElement(librarySource) == null) {
+    if (context.getResult(librarySource, LIBRARY_ELEMENT8) == null) {
       return null;
     }
     // if library has been already resolved, resolve unit