Create more synthetic kernel objects.

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

Index: pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
index 8957ac05ead5ba8d16e2cea1c354f43854235e55..40eca1aa818cf2a444dfae9ad3eeb0441d5990d9 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
@@ -904,6 +904,12 @@ class KernelIfStatement extends IfStatement implements KernelStatement {
   }
 }
 
+/// Concrete shadow object representing an assignment to a target for which
+/// assignment is not allowed.
+class KernelIllegalAssignment extends KernelComplexAssignment {
+  KernelIllegalAssignment(Expression rhs) : super(rhs);
+}
+
 /// Concrete shadow object representing an assignment to a target of the form
 /// `a[b]`.
 class KernelIndexAssign extends KernelComplexAssignmentWithReceiver {