Reapply 47ecf72 after it was reverted in e431e93e872d9a1c97a5177ebb09d5416f1d659a.

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

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index dbff10ebee74a66d83473c08b8d2c53d74dbab38..b4059812a9e3ae697a622fb654871910ef1cf940 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -3969,6 +3969,9 @@ abstract class ExecutableElementImpl extends ElementImpl
 
   @override
   String get documentationComment {
+    if (_kernel != null) {
+      return _kernel.documentationComment;
+    }
     if (serializedExecutable != null) {
       return serializedExecutable?.documentationComment?.text;
     }
@@ -7570,6 +7573,9 @@ abstract class NonParameterVariableElementImpl extends VariableElementImpl {
 
   @override
   String get documentationComment {
+    if (_kernel != null) {
+      return _kernel.documentationComment;
+    }
     if (_unlinkedVariable != null) {
       return _unlinkedVariable?.documentationComment?.text;
     }