Add *IndexSetIfNull methods to SemanticSendVisitor.

pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart

Index: pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart
diff --git a/pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart b/pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart
index 9628684e3f34fd1a2db904e8c79ede3eac5ec089..468aa72e340f1d2a79209081f70ba770ee0736ec 100644
--- a/pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart
+++ b/pkg/compiler/lib/src/inferrer/simple_types_inferrer.dart
@@ -949,6 +949,19 @@ class SimpleTypeInferrerVisitor<T>
   }
 
   @override
+  T visitIndexSetIfNull(
+      ast.SendSet node,
+      ast.Node receiver,
+      ast.Node index,
+      ast.Node rhs,
+      _) {
+    T receiverType = visit(receiver);
+    T indexType = visit(index);
+    T rhsType = visit(rhs);
+    return handleCompoundIndexSet(node, receiverType, indexType, rhsType);
+  }
+
+  @override
   T visitSuperIndexPrefix(
       ast.Send node,
       MethodElement getter,
@@ -996,6 +1009,17 @@ class SimpleTypeInferrerVisitor<T>
   }
 
   @override
+  T visitSuperIndexSetIfNull(
+      ast.SendSet node,
+      MethodElement getter,
+      MethodElement setter,
+      ast.Node index,
+      ast.Node rhs,
+      _) {
+    return handleSuperCompoundIndexSet(node, index, rhs);
+  }
+
+  @override
   T visitUnresolvedSuperCompoundIndexSet(
       ast.Send node,
       Element element,
@@ -1007,6 +1031,16 @@ class SimpleTypeInferrerVisitor<T>
   }
 
   @override
+  T visitUnresolvedSuperIndexSetIfNull(
+      ast.Send node,
+      Element element,
+      ast.Node index,
+      ast.Node rhs,
+      _) {
+    return handleSuperCompoundIndexSet(node, index, rhs);
+  }
+
+  @override
   T visitUnresolvedSuperGetterCompoundIndexSet(
       ast.SendSet node,
       Element element,
@@ -1019,6 +1053,17 @@ class SimpleTypeInferrerVisitor<T>
   }
 
   @override
+  T visitUnresolvedSuperGetterIndexSetIfNull(
+      ast.SendSet node,
+      Element element,
+      MethodElement setter,
+      ast.Node index,
+      ast.Node rhs,
+      _) {
+    return handleSuperCompoundIndexSet(node, index, rhs);
+  }
+
+  @override
   T visitUnresolvedSuperSetterCompoundIndexSet(
       ast.SendSet node,
       MethodElement getter,
@@ -1031,6 +1076,17 @@ class SimpleTypeInferrerVisitor<T>
   }
 
   @override
+  T visitUnresolvedSuperSetterIndexSetIfNull(
+      ast.SendSet node,
+      MethodElement getter,
+      Element element,
+      ast.Node index,
+      ast.Node rhs,
+      _) {
+    return handleSuperCompoundIndexSet(node, index, rhs);
+  }
+
+  @override
   T visitUnresolvedSuperIndexPrefix(
       ast.Send node,
       Element element,