Avoid triggering an assert

runtime/vm/kernel.h

Index: runtime/vm/kernel.h
diff --git a/runtime/vm/kernel.h b/runtime/vm/kernel.h
index a6aae20ab6bcee7f1ee26b821c1be80174242be3..be32218552529f33896c792b4a3ba29b4665234d 100644
--- a/runtime/vm/kernel.h
+++ b/runtime/vm/kernel.h
@@ -935,7 +935,11 @@ class FunctionNode : public TreeNode {
   DartType* return_type() { return return_type_; }
 
   Statement* body() { return body_; }
-  void set_body(Statement* body) { body_ = body; }
+  void set_body(Statement* body) {
+    // Use static_cast to invoke the conversion function and so avoid triggering
+    // ASSERT(pointer_ == NULL) in operator= when overwriting a non-NULL body.
+    static_cast<Statement*&>(body_) = body;
+  }
 
   TokenPosition position() { return position_; }
   TokenPosition end_position() { return end_position_; }