Add *IndexSetIfNull methods to SemanticSendVisitor.

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 8c8f78c5e171a76f809138a700f6ea1714154201..ad5905ddec5d361ca15ca2d70bd0a062bf236dea 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -1037,6 +1037,7 @@ class SwitchCaseJumpHandler extends TargetJumpHandler {
 class SsaBuilder extends ast.Visitor
     with BaseImplementationOfCompoundsMixin,
          BaseImplementationOfSetIfNullsMixin,
+         BaseImplementationOfSuperIndexSetIfNullMixin,
          SemanticSendResolvedMixin,
          NewBulkMixin,
          ErrorBulkMixin
@@ -7108,6 +7109,32 @@ class SsaBuilder extends ast.Visitor
   }
 
   @override
+  handleSuperIndexSetIfNull(
+      ast.SendSet node,
+      Element indexFunction,
+      Element indexSetFunction,
+      ast.Node index,
+      ast.Node rhs,
+      arg,
+      {bool isGetterValid,
+       bool isSetterValid}) {
+    handleCompoundSendSet(node);
+  }
+
+  @override
+  visitIndexSetIfNull(
+      ast.SendSet node,
+      ast.Node receiver,
+      ast.Node index,
+      ast.Node rhs,
+      arg,
+      {bool isGetterValid,
+       bool isSetterValid}) {
+    generateIsDeferredLoadedCheckOfSend(node);
+    handleIndexSendSet(node);
+  }
+
+  @override
   handleTypeLiteralConstantSetIfNulls(
       ast.SendSet node,
       ConstantExpression constant,