Add line starts into unlinked units.

pkg/analyzer/lib/src/summary/summarize_elements.dart

Index: pkg/analyzer/lib/src/summary/summarize_elements.dart
diff --git a/pkg/analyzer/lib/src/summary/summarize_elements.dart b/pkg/analyzer/lib/src/summary/summarize_elements.dart
index e25da271b80a4c88e9f672c500fbf8193c5373bf..607bac4afab44d244171e4d58d1b957d7757fea8 100644
--- a/pkg/analyzer/lib/src/summary/summarize_elements.dart
+++ b/pkg/analyzer/lib/src/summary/summarize_elements.dart
@@ -12,6 +12,7 @@ import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/dart/element/type.dart';
+import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
@@ -450,6 +451,9 @@ class _CompilationUnitSerializer {
     }
     unlinkedUnit.variables = variables;
     unlinkedUnit.references = unlinkedReferences;
+    unlinkedUnit.lineStarts =
+        compilationUnit.context?.getLineInfo(unitSource)?.lineStarts ??
+            const <int>[];
     linkedUnit.references = linkedReferences;
     unitUri = compilationUnit.source.uri.toString();
   }