Annotate targets of implicit this property gets/sets in inference tests.

pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart

Index: pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart b/pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart
index a81aa4f5ad596d65e752bf9d003eb278030a119b..a39fa40818c651619f4e2d72f925e00052691758 100644
--- a/pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart
@@ -13,6 +13,7 @@ import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
         KernelMethodInvocation,
         KernelPropertyGet,
         KernelPropertySet,
+        KernelThisExpression,
         KernelVariableDeclaration,
         KernelVariableGet,
         KernelVariableSet;
@@ -284,12 +285,13 @@ class ThisPropertyAccessor extends Accessor {
       : super(helper, token);
 
   Expression _makeRead(KernelComplexAssignment complexAssignment) =>
-      new KernelPropertyGet(new ThisExpression(), name, getter)
+      new KernelPropertyGet(new KernelThisExpression(), name, getter)
         ..fileOffset = offsetForToken(token);
 
   Expression _makeWrite(Expression value, bool voidContext,
       KernelComplexAssignment complexAssignment) {
-    return new KernelPropertySet(new ThisExpression(), name, value, setter)
+    return new KernelPropertySet(
+        new KernelThisExpression(), name, value, setter)
       ..fileOffset = offsetForToken(token);
   }
 }