Add *IndexSetIfNull methods to SemanticSendVisitor.

tests/compiler/dart2js/semantic_visitor_test_send_data.dart

Index: tests/compiler/dart2js/semantic_visitor_test_send_data.dart
diff --git a/tests/compiler/dart2js/semantic_visitor_test_send_data.dart b/tests/compiler/dart2js/semantic_visitor_test_send_data.dart
index 51eae03565bd11dea569b18019811221035838fa..b72e47964986159be3b02dc0d15ef125e501db33 100644
--- a/tests/compiler/dart2js/semantic_visitor_test_send_data.dart
+++ b/tests/compiler/dart2js/semantic_visitor_test_send_data.dart
@@ -2142,6 +2142,66 @@ const Map<String, List<Test>> SEND_TESTS = const {
                     error: MessageKind.NO_SUPER_IN_STATIC,
                     index: '42',
                     operator: '--')),
+    const Test(
+        '''
+        m() => [][42] ??= 0;
+        ''',
+        const Visit(VisitKind.VISIT_INDEX_SET_IF_NULL,
+                    receiver: '[] ',
+                    index: '42',
+                    rhs: '0')),
+    const Test.clazz(
+        '''
+        class B {
+          operator [](_) => null;
+          operator []=(a, b) {}
+        }
+        class C extends B {
+          m() => super[42] ??= 0;
+        }
+        ''',
+        const Visit(VisitKind.VISIT_SUPER_INDEX_SET_IF_NULL,
+                    getter: 'function(B#[])',
+                    setter: 'function(B#[]=)',
+                    index: '42',
+                    rhs: '0')),
+    const Test.clazz(
+        '''
+        class B {
+          operator []=(a, b) {}
+        }
+        class C extends B {
+          m() => super[42] ??= 0;
+        }
+        ''',
+        const Visit(VisitKind.VISIT_UNRESOLVED_SUPER_GETTER_INDEX_SET_IF_NULL,
+                    setter: 'function(B#[]=)',
+                    index: '42',
+                    rhs: '0')),
+    const Test.clazz(
+        '''
+        class B {
+          operator [](_) => null;
+        }
+        class C extends B {
+          m() => super[42] ??= 0;
+        }
+        ''',
+        const Visit(VisitKind.VISIT_UNRESOLVED_SUPER_SETTER_INDEX_SET_IF_NULL,
+                    getter: 'function(B#[])',
+                    index: '42',
+                    rhs: '0')),
+    const Test.clazz(
+        '''
+        class B {
+        }
+        class C extends B {
+          m() => super[42] ??= 0;
+        }
+        ''',
+        const Visit(VisitKind.VISIT_UNRESOLVED_SUPER_INDEX_SET_IF_NULL,
+                    index: '42',
+                    rhs: '0')),
   ],
   'Equals': const [
     // Equals