[element model] migrate assigned_variables_test

Change-Id: Ib67e86ba6e4165651031e1f4c99298a4a6a83d27
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/401866
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

pkg/analyzer/analyzer_use_new_elements.txt

@@ -162,7 +162,6 @@ test/generated/elements_types_mixin.dart
 test/generated/non_error_resolver_test.dart
 test/generated/resolver_test_case.dart
 test/generated/type_system_test.dart
-test/id_tests/assigned_variables_test.dart
 test/id_tests/type_constraint_generation_test.dart
 test/src/dart/analysis/index_test.dart
 test/src/dart/analysis/result_printer.dart

pkg/analyzer/test/id_tests/assigned_variables_test.dart

@@ -37,11 +37,10 @@ class _AssignedVariablesDataComputer extends DataComputer<_Data> {
   @override
   void computeUnitData(TestingData testingData, CompilationUnit unit,
       Map<Id, ActualData<_Data>> actualMap) {
-    var unitElement = unit.declaredElement!;
-    var flowResult = testingData.uriToFlowAnalysisData[unitElement.source.uri]!;
-    _AssignedVariablesDataExtractor(
-            unitElement.source.uri, actualMap, flowResult)
-        .run(unit);
+    var unitElement = unit.declaredFragment!.element;
+    var uri = unitElement.firstFragment.source.uri;
+    var flowResult = testingData.uriToFlowAnalysisData[uri]!;
+    _AssignedVariablesDataExtractor(uri, actualMap, flowResult).run(unit);
   }
 }