Issue 29288. Resynthesize Import/Export/PartElement for every directive.

pkg/analyzer/test/src/dart/analysis/index_test.dart

Index: pkg/analyzer/test/src/dart/analysis/index_test.dart
diff --git a/pkg/analyzer/test/src/dart/analysis/index_test.dart b/pkg/analyzer/test/src/dart/analysis/index_test.dart
index 51fb995a9a4a7e86af1113316619843540afdb1e..ffa365d1f01d709c9d3ee3e7538090bbf6e0ae20 100644
--- a/pkg/analyzer/test/src/dart/analysis/index_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/index_test.dart
@@ -476,6 +476,20 @@ part 'my_unit.dart';
     assertThat(element)..isReferencedAt("'my_unit.dart';", true, length: 14);
   }
 
+  test_isReferencedBy_CompilationUnitElement_part_inPart() async {
+    provider.newFile(_p('$testProject/a.dart'), 'part of lib;');
+    provider.newFile(
+        _p('$testProject/b.dart'),
+        '''
+library lib;
+part 'a.dart';
+''');
+    await _indexTestUnit('''
+part 'b.dart';
+''');
+    // No exception, even though a.dart is a part of b.dart part.
+  }
+
   test_isReferencedBy_ConstructorElement() async {
     await _indexTestUnit('''
 class A implements B {